Unexpected B/Al Transelementation within a Rh Pincer Complex.

We report the synthesis of PAlP and PBP pincer complexes of Rh with a central bis(N-pyrrolyl)aluminyl or -boryl unit. Complex (PAlpyP)Rh(CO)2 possesses an aluminyl site stabilized by coordination of pyridine, resulting in a four-coordinate Al. Attempts to access the three-coordinate aluminyl by abstraction of pyridine with BF3·Et2O unexpectedly led to a B/Al metathesis with the preservation of the pincer structure in the product (PBP)Rh(CO)2. Abstraction of pyridine was carried out using B(C6F5)3, but the desired (PAlP)Rh(CO)2 underwent dimerization via isocarbonyl bridging.