Hydrodeoxygenative Cyclotetramerization of Carbon Monoxide by a Trinuclear Titanium Polyhydride Complex.

The reductive coupling of carbon monoxide (CO) by metal hydrides is of fundamental interest and practical importance. Herein we report an unprecedented hydrodeoxygenative cyclotetramerization of CO by a trinuclear titanium polyhydride complex [(C5Me4SiMe3)Ti]3(μ3-H)(μ2-H)6 (1). The reaction of CO with 1 at -78 °C gave an ethen-1,2-diyl species [CH═CH]2- through the hydrodeoxygenative dimerization of two molecules of CO, which upon cycloaddition to another two molecules of CO afforded a cyclobuten-3,4-diyl-1,2-diolate unit [C4H2O2]4-. The hydrogenolysis of the [C4H2O2]4- species with H2 yielded a tetrahydrocyclobuten-1,2-diolate species [C4H4O2]2-, which on heating at 100 °C gave a cyclobuten-2-yl-1-olate product [C4H4O]2-. The acidolysis of the [C4H2O2]4- and [C4H4O]2- species with HCl afforded γ-butyrolactone and cyclobutanone, respectively.