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)Ti3(μ3-H)(μ2-H)6 (1). The reaction of CO with 1 at −78 °C gave an ethen-1,2-diyl species CH═CH2– 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 C4H2O24–. The hydrogenolysis of the C4H2O24– species with H2 yielded a tetrahydrocyclobuten-1,2-diolate species C4H4O22–, which on heating at 100 °C gave a cyclobuten-2-yl-1-olate product C4H4O2–. The acidolysis of the C4H2O24– and C4H4O2– species with HCl afforded γ-butyrolactone and cyclobutanone, respectively.