Phosphorus-nitrogen compounds- (Part 50): correlations between structural parameters for cylophosphazene derivatives containing ferrocenyl pendant arm(s).

The results of a systematic study of spiro -cyclotri/tetraphosphazenes with ferrocenyl pendant arm on the basis of correlation between structural parameters were presented. The main parameters were obtained from Xray crystallography and 31P NMR results in order to investigate the relationship between the δ P spiro shift values and endocyclic and exocyclic NPN bond angles, and electron density transfer parameters. Structural parameters derived from 11 types of the ferrocenyl cyclophosphazene derivatives with 5- to 7-membered spiro -rings introduced to the literature from our research group were studied and compared with each other.

1. Introduction

The class="Chemical">phosphazene chemistry has attracted much attention since 1960 [1,2]. Esclass="Chemical">pecially, class="Chemical">pan class="Chemical">hexachlorocyclotriphosphazene (N3P3Cl6, trimer) and octachlorocyclotetraphosphazene (N4P4Cl8, tetramer) are of particular interest to both theoretical and experimental researchers concerning phosphazene-based chemistry. Because of their tendency to react with the nucleophilic mono-, di-, or multi-functional groups [3-6], both of the cyclophosphazenes were used in the syntheses of a considerable range of organocyclotri/tetraphosphazene derivatives with diverse applications [7,8]. The substantial efforts have been performed on the nucleophilic substitution reactions, in which the 1- to 6-Cl-atoms on trimer and 1- to 8-Cl atoms on tetramer have been replaced by the NH and/or OH functioned reagents, forming isomeric products e.g., structural ( spiro -, ansa - and bino -architectures or a mixed of the same or different architectures), geometrical (geminal, non-geminal cis/trans -), and optical isomers [9,10]. The nature of the products strongly depends on the various chemical factors which control the replacement reaction mechanisms such as chain lengths of nucleophilic groups, the polarity of solvents, and the reaction temperature [11]. So far only a limited number of published studies on cyclophosphazene derivatives with ferrocenyl pendant arm is present in the literature [12-16].

The class="Chemical">organocyclophosphazene derivatives have several class="Chemical">potential aclass="Chemical">pclass="Chemical">plications in difclass="Chemical">pan class="Chemical">ferent fields of science as flame-retardant additives for organic polymers [17], liquid crystals [18,19], antibacterial [20] and anti-cancer [21] agents, fluorescence chemosensors [22], ion-transferring agents for rechargeable lithium batteries [23,24] and light-emitting diodes (LEDs) [25]. Besides, ferrocene-containing compounds have been used for molecular sensors, biosensors, electron-transfer mediators, non-linear optical materials, liquid crystals, and redox-active probe materials [26,27]. In this context, we were therefore interested in synthesizing of ferrocenyl cyclophosphazenes and thought that the presence of both ferrocene moiety as a substituent and a trimeric/tetrameric phosphazene as a skeleton in a molecule could give rise to a novel kind of cyclophosphazene derivatives and bring together many biological and physicochemical properties of the molecule. Furthermore, cyclotri/tetraphosphazene ring systems are electrochemically inert, and ferrocenyl group is an excellent redox-active precursor. Hence, ferrocenyl cyclophosphazenes were synthesized to investigate the electrochemical behavior of the phosphazenes [28-30]. Furthermore, substituted spiro -monoferrocenyl cyclotri/tetraphosphazenes were prepared by our group to evaluate in terms of their antituberculosis, anticancer, and antimicrobial activities. According to these studies, it was observed that geminal vanillinato (Van)-substituted spiro -monoferrocenyl cyclotriphosphazenes [31], tetra pyrrolidine (Pyr)-substituted spiro -mono [32,33] and bisferrocenyl [33] cyclotriphosphazenes and hexa Pyr-substituted spiro -monoferrocenyl cyclotetraphosphazenes [34] inhibited the growth of Mycobacterium tuberculosis H37Rv. While 1,4-dioxa-8-aza spiro [4,5]decane (DASD)-substituted spiro -bisferrocenyl [35] and partly substituted di spiro -bisferrocenyl [36] cyclotriphosphazenes, the fully and nongeminal (cis) [37] Van-substituted spiro -monoferrocenyl cyclotriphosphazenes, were effective against the human cervical cancer cell line (HeLa), bis(diamino) substituted di spiro -bisferrocenyl cyclotetraphosphazene was found to be more active against colon cancer DLD-1 cells than Doxorubicin [38]. It was also found that the DASD and Pyr-substituted ferrocenyl cyclotriphosphazenes were active against some gram-positive and gram-negative bacteria [32,33,35] and Pyrsubstituted ferrocenyl cyclotetraphosphazenes were more effective than the commercial antifungal drug Ketoconazole against fungi [34].

Besides, the chiral properties of mono class="Chemical">Van-substituted di class="Chemical">pan class="Chemical">spiro -bis ferrocenyl cyclophosphazenes were investigated by 31P NMR spectroscopy upon the addition of the chiral solvating agent [39].

On the other hand, we also succeeded in the preparation of ultrathin and highly ordered Langmuir-Blodgett films of class="Chemical">tetrachloro-, and mono and class="Chemical">pan class="Chemical">gem DASD-substituted mono-ferrocenyl cyclotriphosphazenes [40,41]. These compounds are the first phosphazene derivatives prepared as thin films in the literature.

Shaw described the first systematic study of the relationship between the bond angles around the class="Disease">phosphorus atoms and class="Chemical">pan class="Chemical">31P NMR spectral data in phosphazene derivatives [42]. The changes in structural parameters for different kinds of structurally analogous cyclotriphosphazenes (cyclotriphosphazenes possessing 6-membered spiro ring/rings [43], mono spiro -, di spiro -, spiro - ansa - spiro - and spiro - bino - spiro -cyclotriphosphazenes [44-46], spiro -cyclotriphosphazenic lariat (PNP-pivot) ether derivatives [47,48], monotopic and ditopic spiro -crypta cyclotriphosphazenes [49-51]) were investigated previously. It was found that the systematic variations in the 31P NMR chemical shifts depend fundamentally on some electronic (electron-releasing and electron-withdrawing capacities of substituent groups), steric (the steric hindrance between the exocyclic groups) and conformational factors, and on the changes in bond lengths and bond angles around the phosphorus atoms [especially endocyclic (α) and exocyclic (α′) bond angles] in cyclotriphosphazene derivatives. The current study deals with a number of correlations between structural parameters [e.g., 31P NMR spectral data and X-ray crystallographic data (endocyclic and exocyclic NPN bond angles, and bond lengths)] in spiro cyclic ferrocenyl cyclophosphazenes introduced to the literature from our research group (Table 1) [33-41,52]. Therefore the content of this report includes: (i) a brief description of the synthesis methods of 11 different structural types and a total of 28 spiro cyclic ferrocenyl phosphazenes with 5- to 7−membered spiro -rings used for the graph construction, (ii) the relationship between the δ P shifts and the values of electron density transfer parameters Δ(P–N), and (iii) the correlation of δ P shifts and endocyclic (α) and exocyclic (α′) NPN bond angles of the compounds.

The endocyclic (α) and exocyclic (α′) pan class="Gene">NPN bond angles and bond lengths (a, a′ , b, and b′) on the formulae of class="Chemical">pan class="Chemical">cyclophosphazenes.

2. Results and discussion

2.1. Syntheses

Routes for the synthesis of class="Chemical">spiro class="Chemical">pan class="Chemical">cyclic ferrocenyl cyclophosphazenes clarified their solid-state structures using X-ray crystallography by our research group and investigated in this study are summarized in Scheme. The syntheses of mono and bisferrocenyl diamines, as the starting compounds, were carried out according to the published procedures, in which ferrocenecarboxaldehyde reacted with appropriate diamines and followed by reduction of the azomethine bonds in the intermediate products [53,54]. The reactions of trimer with mono and bisferrocenyl diamines gave partly substituted spiro -mono ( I ) [33] and spiro -bis ( V ) [33,52] ferrocenyl cyclotriphosphazenes, respectively. The substituted phosphazene derivatives were synthesized by stepwise substitutions of partly substituted spiro -mono ( I ) and spiro -bis ( V ) ferrocenyl cyclotriphosphazenes which consist of 4 reactive P-Cl units. The reactions of 1 equimolar amount of partly substituted spiro -bis ( V ) and spiro mono ( I ) ferrocenyl cyclotriphosphazenes with 1 and 2 equimolar amounts of heterocyclic amines (DASD and Pyr) produced corresponding mono heterocyclic amine (DASD) substituted spiro -bis (VI) [35] and spiro -mono ( II ) [40] and geminal heterocyclic amine (DASD and Pyr) substituted spiro -bis ( VII ) [35] and spiro -mono ( III ) [35,40,41] ferrocenyl cyclotriphosphazenes in the presence of NEt3 in refluxing dry THF. The fully heterocyclic amine [DASD, Pyr, and morpholine (Morp)] substituted spiro -bis ( V ) [33] and spiro -mono ( I ) [33,35,52] ferrocenyl cyclotriphosphazenes were prepared by replacing 4 Cl-atoms on partly substituted derivatives ( I ) and ( V ), respectively, with excess heterocyclic amines in boiling THF. The reactions of equimolar amounts of partly substituted spiro -mono ferrocenyl cyclotriphosphaze ( I ) and potassium vanillinate were found to yield the corresponding mono Van-substituted spiro -mono ferrocenyl cyclotriphosphaze ( III ) as a major product and geminal ( III ) [37] and nongeminal (cis) ( IV ) substituted spiro -mono ferrocenyl cyclotriphosphazenes as minor products. Fully Van-substituted spiro -bisferrocenyl cyclotriphosphazene ( V ) was synthesized from the reaction carried out with excess potassium vanillinate [37]. The Cl-replacement reactions of trimer with 2 equimolar amounts of mono-ferrocenyldiamines resulted in the formation of the corresponding partly substituted cis- (meso) and trans-(racem) di spiro -bisferrocenyl cyclotriphosphazenes ( VIII ) as the major products and spiro -mono ( I ) ferrocenyl cyclotriphosphazenes as minor products [36]. Three products were separated performing column chromatography. The reactions of 1 equimolar amount of cis- and trans-di spiro -bisferrocenyl cyclotriphosphazenes ( VIII ) having 2 reactive Cl-atoms with 2 equimolar amounts of potassium vanillinate in refluxing THF afforded the mono ( IX ) and fully ( VIII ) Van-substituted cis- and trans-di spiro -bisferrocenyl cyclotriphosphazenes ( IX ) and ( VIII ) [39]. The mono and fully substituted derivatives were separated using column chromatography. On the other hand, the partly substituted spiro -mono ( X ) [34] and cis- and trans-di spiro -bis ( XI ) [38] ferrocenyl cyclotetraphosphazenes were obtained from the reactions of tetramer with 1 and 2 equimolar amounts of monoferrocenyl diamines in dry THF. The fully Pyr-substituted ( X ) and trans-( XI ) were prepared by the reaction of partly substituted ones with excess Pyr in dry THF at ambient temperature.

Routes for the synthesis of pan class="Chemical">spirocyclic ferrocenyl cyclophosphazene derivatives investigated in this study.

2.2. Correlations between structural parameters

The endocyclic (α) and exocyclic (α′) class="Gene">NPN bond angles, and the bond lengths (a, a′ , b, and b′) were defined in the generalized structures for the 11 tyclass="Chemical">pes of class="Chemical">pan class="Chemical">cyclotri/tetraphosphazenes containing ferrocenyl pendant arm/arms and 5-, 6- and 7-membered spiro -ring/rings shown in Table 1. δPs piro shifts, α, and α′ bond angles, and Δ(P–N) values that are needed to be used for graph construction are listed in Table 2. The corresponding values of the standard compounds trimer (N3 P3 Cl6) [55,56] and tetramer (N4 P4 Cl8) [57,58] were taken from the literature. Types I and V members are partly and fully substituted spiro -mono and spiro -bisferocenyl cyclotriphosphazenes, respectively. Mono and geminal substituted spiro -mono/bisferocenyl cyclotriphosphazenes are the types II and VI , and the types III and VII group members, respectively. Nongeminal (cis) substituted spiro -monoferocenyl cyclotriphosphazene constitutes the type IV . Members of types VIII and IX derivatives comprise partly and fully substituted and monosubstituted cis/trans -di spiro -bisferocenyl cyclotriphosphazenes, respectively. spiro -Mono and trans -di spiro -bisferocenyl cyclotetrahosphazenes constitute the types X and XI compounds.

Endocyclic (α) and exocyclic (α′) class="Gene">NPN bond angles, bond lengths (a, a′, b, and b′), δclass="Chemical">pan class="Chemical">P shifts and Δ(P-N) values for the compounds [δPshifts in ppm, α and α′ angles in °, a, a′, b, and b′ lengths in Å].

The concept of the double-bond character of the class="Chemical">P-N linkage in the class="Chemical">pan class="Chemical">cyclophosphazene derivatives is still not clearly understood. Negative hyperconjugation and ionic bonding alternatives are exclusive [59]. The natural bond orbital and topological electron-density analyses of phosphazenes have proved the crucial role of negative hyperconjugation in the description of the P-N bond.

2.2.1. The correlation of δ P shifts and values of electron density transfer parameters Δ(P–N)

The electron density transclass="Chemical">fer class="Chemical">parameter Δ(class="Chemical">pan class="Chemical">P–N) is the difference between the bond lengths of 2 adjacent endocyclic P-N bonds as defined in Table 2 for spiro cyclic ferrocenyl phosphazenes. It shows a measure of the electron releasing and withdrawing capacities of the substituent groups on cyclophosphazene ring. The relationship between the δ P shifts and Δ(P–N) values is illustrated in Figure 1 for partly and heterocyclic amine [Pyr, piperidine (Pip), Morp and DASD) (i) and Van (ii) substituted spiro cyclic ferrocenyl phosphazenes, respectively. A cluster of points rather than the linear trend was observed between the Δ(P–N) and δ P shifts. In Figure 1i, all types of triphosphazene structures were accumulated in 6 regions A, B, C, D, E, and F. The points of partly substituted types ( I and V ) and type VIII phosphazenes accumulate in regions A and B, respectively. The points of mono (types II and VI ), geminal (types III and VII ) and fully heterocyclic amine substituted cyclotri (types I and V ) and cyclotetra (type X) phosphazenes accumulate in regions C, D, E, and F, respectively.

The relationship between δ class="Chemical">P shifts and Δ(class="Chemical">pan class="Chemical">P-N) values for partly and heterocyclic amine (Pyr, Pip, Morp, DASD) (i) and Van (ii) substituted spiro cyclic ferrocenyl phosphazenes. δ PClPCl shift values of N3P3Cl6 and N4P4Cl8 are 19.60 [56] and –5.45 [58] ppm, respectively.

According to Figure 1i, some comparisons can be made on the electron-releasing power of the substituent depending on whclass="Chemical">ether the substituent is a class="Chemical">pan class="Chemical">chloro or heterocyclic amine group of the compounds with the same membered spiro -rings. For example, the Δ(P–N) values of fully heterocyclic amine substituted I d, V c, and b are respectively; 0.0055, 0.0035, and –0.005 and –0.0055, indicating that the electron releasing power of the nitrogen atoms of heterocyclic amine groups is greater than that of the chloro groups in Ia (0.087), V b (0.0675), and a (0.046) with the larger Δ(P–N) values. A similar situation is observed for fully Van ( V d and d) and partly [ V a and ( a and b)] substituted ferrocenyl cyclophosphazenes (Figure 1ii), showing the oxygen atoms of Van groups bonded to phosphorus atoms release electrons to the cyclophosphazene ring. It is not possible to say whether heterocyclic amines or vanniline release more electrons to the phosphazene ring since we do not have crystallographic data of the heterocyclic amines and Van substituted derivatives of any type are not available.

Moreover, there is no significant difclass="Chemical">ference between the Δ(class="Chemical">pan class="Chemical">P–N) values of cis- and trans -structures of the same compound for types VIII and IX phosphazenes (0.00825 for VIII b, 0.002475 for VIII c, and 0.01095 for IX a). However, the difference between the Δ(P–N) values of cis- and trans -structures of the phosphazenes with 5-membered spiro -rings ( VIII b and IX a) is slightly larger than that of the phosphazene with 6-membered spiro -rings ( VIII c). That could be significantly attributed to the fact that 5-membered spiro -rings of b, b, and are in envelope conformation and 6-membered spiro -rings of c and c are in the chair conformation [36,39].

For fully class="Chemical">heterocyclic amine substituted class="Chemical">pan class="Chemical">phosphazenes (cycle E), the Δ(P–N) and δ P values of cyclotriphosphazenes having the 7-membered spiro -ring ( I d and V c) are similar, regardless of whether the compounds are mono (type I ) and bis (type V ) ferrocenyl phosphazenes.

It can be seen from Figure 1i that there are greater changes in Δ(class="Chemical">P–N) values for tyclass="Chemical">pes II and VI with 1 class="Chemical">pan class="Chemical">heterocyclic amine substituent per P atom, types III and VII with 2 heterocyclic amine substituents per P atom and types I and V with 4 heterocyclic amine substituents. Therefore, the Δ(P–N) values of these types phosphazenes can be compared with each other according to the number of heterocyclic amine substituents. As expected, the Δ(P–N) value of mono substituted compounds is between the Δ(P–N) value of partly (cycle A) and fully (cycle E) substituted phosphazenes, while geminal substituted derivatives except for VII a (cycle D) have the Δ(P–N) value between those of mono (cycle C) and fully (cycle E) substituted ones. The Δ(P–N) value of VII a appears to the left more than other geminal substituted derivatives ( III a- III c) (cycle D) or is greater than those of the fully substituted derivatives (cycle E). This situation may be related to the higher basicity of the DASD substituent in VII a. A similar relationship was observed between the Δ(P–N) values of nongeminal cis - ( IV a) and fully ( V d) Van substituted cyclophosphazenes and partly substituted I a and V a, respectively (Figure 1ii). Furthermore, the Δ(P–N) values of fully heterocyclic amine substituted types X (cycle F) and XI cyclotetraphosphazenes and types I and V cyclotriphosphazenes, respectively, are quite close together.

Although the compounds III a and VII a both have class="Chemical">geminal structure and 7-membered class="Chemical">pan class="Chemical">spiro -ring, and are close in δ P shifts, the major difference in their Δ(P–N) values and basicities is that the phosphazenes contain mono and bis ferrocenyl pendant arms, respectively. On the other hand, based on the electron-releasing capacity of the ferrocenyl pendant group for partly substituted phosphazenes (cycles A and B), it has been made the following order: Type VIII >type V >type I . Type I ( Ia ), and type V compounds ( Va and Vb ) are mono- spiro mono and bis structures, while type VIII ( , , and ) phosphazenes are di- spiro bis structures. As expected, the electron releasing powers of 2 ferrocenyl pendant groups are greater than those of 1 ferrocenyl pendant group. Moreover, in partly substituted phosphazenes (cycle A), the δ P shifts of 7-membered Ia and Vb are close to each other while 6-membered Va has a lower δ P shift.

In the case of 5-membered class="Chemical">spiro -ring class="Chemical">pan class="Chemical">geminal ( IIIb and IIIc ) and 6-membered spiro -ring fully ( Ib and Ic ) substituted phosphazenes, the electron releasing capacity of DASD group is much larger than that of Pip and Pyr, respectively.

Besides, when the number of atoms increases in the class="Chemical">spiro -ring, the electron releasing caclass="Chemical">pacity of the class="Chemical">pan class="Chemical">phosphazene decreases. In general, the electron releasing power of the rings is in the following order: spiro -rings with 5-membered > spiro -rings with 6-membered > spiro -rings with 7-membered.

As a result, electron−withdrawing substituents, like class="Chemical">chlorine grouclass="Chemical">p, increase Δ(class="Chemical">pan class="Chemical">P–N) values, pulling away electrons from spiro -ring/rings to the phosphorus atom bonded to the electron−withdrawing groups. Whereas the electron-releasing substituents, like heterocyclic amines, decrease Δ(P–N) values, resulting in decreased the bond lengths a and a′ and increased the bond lengths b and b′ when compared bond lengths of partly substituted derivatives. Hence, the shortening of the endocyclic P–N bonds and decreased electron charge density at the exocyclic P-N bonds is likely to be a measure of the electron-releasing power of the substituent and the increase in negative hyperconjugation.

The relationship between the Δ(class="Chemical">P–N) and δ class="Chemical">pan class="Chemical">P shifts makes sense in the basicity of the ring nitrogen atoms in phosphazenes. The basicity of the chlorocyclophosphazene ring nitrogen atoms is quite low, and it may be improved by replacing Cl-atoms with electron-releasing substituents on phosphorus. Thus, the basicity of the phosphazene ring nitrogen atoms (N1-PX2 and N2-P) in fully substituted cyclotriphosphazenes with those in partly substituted ones can be compared. The basicity of N1 atom/atoms in fully substituted phosphazenes appears to have increased due to electron-releasing power of the heterocyclic amine groups, while N2 atom/atoms in partly substituted phosphazenes due to electron-withdrawing power of the chloro groups. As a result, an increase in the electron-releasing power of heterocyclic amine substituents seems to bring about an increase in the basicity of the nitrogen atom (N1) and the negative hyperconjugation.

2.2.2. The correlation of the δ P shifts, endocyclic (α), and exocyclic (α′ ) NPN bond angles

A cluster of points between the δ class="Chemical">P class="Chemical">pan class="Chemical">spiro shifts and the endocyclic NPN bond angles (α) [A, B, C, D, E, and F given in Figure 2i)] and a trend of approximate linearity between the δ P spiro shifts and the exocyclic NPN bond angles (α′) [(a), (b), (c), and (d) given in Figure 2ii] were observed.

The relationship between δ class="Chemical">P shifts and endocyclic (α) (i) and exocyclic α ′ (ii) class="Chemical">pan class="Gene">NPN bond angles for partly and heterocyclic amine (Pyr, Pip, Morp, DASD) substituted spiro cyclic ferrocenyl phosphazenes. δ PClPCl shift values of N3P3Cl6 and N4P4Cl8 are 19.60 [56] and –5.45 [58] ppm, respectively. The α and α ′ values are 118.3(2) and 101.2(1)° for N3P3Cl6 [55] and 121.2 and 102.8° for N4 P4 Cl8 [57] respectively.

The changes in α and α′ bond angles show parallelism except for a contrasting trend observed for partly substituted types I and V class="Chemical">cyclotriphosphazenes (cycle A) and fully substitute tyclass="Chemical">pe X class="Chemical">pan class="Chemical">cyclotetraphosphazenes (cycle F). Small changes in α′ bond angles lead to significant changes in δ P spiro shifts. The number of members in the spiro -ring seems to be effective on α′ bond angles. In fact, the α′ bond angles of cyclotriphosphazenes with 5-membered spiro -ring are narrower than those with larger 6- and 7-membered ones and even narrower than the corresponding angle [101.2(1)°] [55] in the standard compound N3P3Cl6. For example, α′ NPN bond angles of the more flexible 7-membered IIIa and VIIa are larger than those of 5-membered counterparts IIIb and IIIc (cycle D given in Figure 2i and line (c) given in Figure 2ii). Likewise, α′ bond angles of 7-( Vb ) and 6-( VIIIc ) membered phosphazenes are wider with respect to the values of 6-( Va ) and 5-( VIIIa and VIIIb ) membered derivatives, respectively. The α and α′ values of IIa are among the α and α′ values of other compounds in cycles A and C (Figure 2i) and line (a) (Figure 2ii) due to its 6-membered spiro -ring, and the α′ value of IIa close to the α′ angle of the standard N3P3Cl6 [101.2(1)°] [55]. As mentioned before, there is a difference between Δ(P–N) values of the phosphazenes IIIa and VIIa having geminal structure and 7-membered spiro -ring and nearly the same δ P spiro shift values. The difference between the α′ and α bond angles of both compounds is ~3 and 1°, and this explains that the α bond angle is less sensitive to the electronic changes. When spiro -bisferocenyl Va and VIa cyclotriphosphazenes are compared, it is seen that the δ P spiro shift value increases from 6.20 to 14.41 ppm by mono substitution, while the α′ bond angle decreases from 105.0(2) to 102.85(11)° and the α bond angle increases from 110.0(2) to 114.42(13)°, respectively, indicating a change in substituent groups causes a major change in both α and α′ bond angles. In fact, the values of α and α′ bond angles of 7-membered partly substituted cyclotriphosphazene (Vb) are larger and smaller than those of the 7-membered heterocyclic amine substituted cyclotriphosphazene ( Vc ). Based on the electron-releasing capacities of the substituents for Vb and vc , electrons are transferred from heterocyclic amine groups to the cyclotriphosphazene ring in Vc and from the cyclotriphosphazene ring to Cl-atoms in Vb . The α and α′ bond angles of fully pyrolidine substituted cyclotetraphosphazenes ( Xa and Xb ) are close to each other, and the angles have the values to be expected for cyclotetraphosphazenes with 5-membered spiro -ring. In addition, the α′ angle of the 5-membered DASD substituted IIIc is larger than that of the 5-membered Pip substituted IIIb , which once again confirms that the DASD substituent has a greater electron-releasing power than the Pip substituent and shows that the electron transferred from the DASD group to the phosphazene ring does not remain only in the phosphazene ring but also transfers towards the spiro -ring. In case of partly and fully substituted type XI cyclotetraphosphazenes, α angle is much affected by the substitution, but, α′ angle is less affected. Moreover, the correlations between the δ P spiro shifts and α (Figure 3i) and α′ (Figure 3ii) NPN bond angles show contrasting trends. For example, the α and α′ angles of 6-( Va ) and 4-( Ia ) membered partly substituted phosphazenes are smaller than 6-membered fully Van-( Vd ) and 4-membered nongeminal cis- ( IVa ) substituted phosphazenes, respectively.

The relationship between δ class="Chemical">P shifts and endocyclic (α) (i) and exocyclic α′ (ii) class="Chemical">pan class="Gene">NPN bond angles for partly and Van substituted spiro cyclic ferrocenyl phosphazenes.

Although there are class="Chemical">few examclass="Chemical">ples of class="Chemical">pan class="Chemical">spiro -ferrocenyl substituted cyclotetraphosphazenes, the structural parameters of these compounds are given in the figures with the aim of comparison purposes. More values are necessary to learn more about the correlations for cyclotetraphosphazenes.

3. Conclusions

A systematic study concerning the correlations between structural parameters [e.g., class="Chemical">31P NMR sclass="Chemical">pectral data and X-ray crystallograclass="Chemical">phic data (endocyclic and exocyclic class="Chemical">pan class="Gene">NPN bond angles, and bond lengths)] displayed some characteristic results for mono- and di- spiro cyclophosphazene derivatives bearing ferrocenyl pendant arm/arms. Naturally, these results become more reliable when more cyclic phosphazenes from this series are synthesized and the 31P NMR spectroscopic and X-ray crystallographic data of these molecules are taken into account. It is necessary to extend the study for other members of the spiro cyclic ferrocenyl cyclophosphazene family to get a more general and including views about the correlations between structural parameters of these molecules. Research along these lines is actually under development in our laboratory and results will be presented elsewhere in the forthcoming future.

Table 1

The endocyclic (α) and exocyclic (α′) NPN bond angles and bond lengths (a, a′ , b, and b′) on the formulae of cyclophosphazenes.

Table 2

Endocyclic (α) and exocyclic (α′) NPN bond angles, bond lengths (a, a′, b, and b′), δP shifts and Δ(P-N) values for the compounds [δPshifts in ppm, α and α′ angles in °, a, a′, b, and b′ lengths in Å].

Compound	a	a'	b	b'	Δ(P-N)	α	α'	ΔPNPN
Ia 33	1.613(3)	1.614(3)	1.548(3)	1.548(3)	0.0870	113.14(15)	102.68(16)	13.62	for ( I-VII ), ( X ) and ( XI ) Δ (P-N) = (a+a')/2-(b+b')/2 for ( VIII ) and ( IX ) Δ (P-N) = (a+a')/2 - b
Ib 33	1.587(3)	1.598(3)	1.603(3)	1.588(2)	-0.003	117.66(13)	102.16(13)	20.76
	1.589(2)	1.600(3)	1.601(3)	1.587(3)	0.0005	117.73(13)	101.86(13)
Ic 35	1.586(1)	1.600(1)	1.602(1)	1.594(1)	-0.005	117.67(17)	103.02(7)	19.38
Id 52	1.604(1)	1.597(1)	1.593(1)	1.597(1)	0.0055	115.47(7)	104.06(7)	22.10
IIa 40	1.630(8)	1.596(8)	1.547(9)	1.566(8)	0.0565	113.7(4)	101.7(4)	17.00
IIIa 35	1.592(1)	1.628(1)	1.592(1)	1.560(1)	0.034	114.62(6)	104.68(6)	17.32
IIIb 41	1.579(3)	1.616(3)	1.598(3)	1.562(3)	0.0175	113.18(15)	93.24(15)	22.06
IIIc 40	1.6208(10)	1.5903(10)	1.5634(10)	1.5921(10)	0.0278	113.32(5)	95.00(5)	21.06
IVa 37	1.612(2)	1.612(2)	1.555(2)	1.556(2)	0.0565	113.50(10)	100.13(10)	15.41
Va 52	1.620(3)	1.620(3)	1.544(3)	1.544(3)	0.076	110.0(2)	105.0(2)	6.20
Vb 33	1.613(3)	1.619(3)	1.549(3)	1.548(3)	0.0675	113.09(13)	103.14(13)	14.56
Vc 33	1.599(4)	1.591(3)	1.592(3)	1.591(4)	0.0035	114.96(18)	98.94(17)	22.08
Vd 37	1.613(3)	1.613(3)	1.563(3)	1.563(3)	0.05	113.3(2)	100.6(2)	21.60
VIa 35	1.592(2)	1.626(2)	1.574(2)	1.554(2)	0.045	114.42(13)	102.85(11)	14.41
VIIa 35	1.558(2)	1.600(2)	1.603(3)	1.593(2)	-0.019	113.26(9)	101.45(9)	18.32
t -VIIIb 36	1.620(4)	1.587(3)	1.555(4)	-	0.0485	113.31(17)	94.49(18)	24.22
	1.610(3)	1.587(3)	1.561(4)	-	0.0375	113.05(17)	94.48(17)
c -VIIIb 36	1.618(3)	1.593(3)	1.552(3)	-	0.0535	112.98(16)	94.33(18)	22.57
	1.620(3)	1.586(3)	1.565(3)	-	0.038	113.25(16)	93.94(18)
t -VIIIb 36	1.614(3)	1.589(3)	1.558(3)	-	0.0435	113.24(16)	94.61(16)	22.63
	1.612(3)	1.589(3)	1.569(3)	-	0.0315	112.23(16)	93.92(16)
c -VIIIc 36	1.634(2)	1.583(2)	1.549(3)	-	0.0595	113.84(13)	102.10(13)	19.63
	1.610(2)	1.594(2)	1.572(3)	-	0.03	115.59(12)	103.91(14)
t -VIIIc 36	1.6055(19)	1.5951(17)	1.5602(19)	-	0.0401	115.57(9)	104.35(10)	19.65
	1.6292(19)	1.5837(17)	1.5585(19)	-	0.04795	114.08(9)	103.63(9)
c -VIIId 39	1.6014(19)	1.588(2)	1.5716(18)	-	0.0231	114.03(10)	95.22(9)	27.32
	1.601(2)	1.5913(19)	1.5647(19)	-	0.03145	113.42(10)	93.39(10)
t -VIIId 39	1.608(3)	1.592(4)	1.566(3)	-	0.034	113.43(17)	93.75(19)	27.52
	1.611(3)	1.586(3)	1.573(3)	-	0.0255	113.56(18)	94.72(18)
c -IXa 39	1.605(2)	1.5922(19)	1.562(2)	-	0.0366	113.64(10)	94.54(10)	26.68
	1.612(2)	1.586(2)	1.563(2)	-	0.036	112.50(10)	93.93(11)
t -IXa 39	1.610(3)	1.593(3)	1.560(4)	-	0.0415	113.77(19)	94.88(18)	25.91
	1.622(3)	1.584(3)	1.550(4)	-	0.053	113.34(18)	93.89(19)
Xa 34	1.587(3)	1.583(3)	1.589(3)	1.586(3)	-0.0025	118.19(15)	94.31(13)	12.61
Xb 34	1.584(2)	1.581(2)	1.592(2)	1.588(2)	-0.0075	117.68(9)	94.94(8)	12.27
XIa 38	1.5940(13)	1.5853(14)	1.5301(13)	1.5570(13)	0.046	114.91(7)	102.01(7)	1.19
XIb 38	1.584(3)	1.573(3)	1.585(3)	1.582(3)	-0.005	121.07(14)	102.14(13)	3.46
	1.582(3)	1.568(3)	1.584(3)	1.577(3)	-0.0055	119.87(14)	102.94(14)