Synthesis, structure, and reactivity of tungsten acetylide-germylene complexes

The novel acetylide-germylene complexes Cp*(CO) ₂W(GePh₂)(CCR) (7a, R = SiMe₃; 7b, R = CMe ₃) were synthesized by the reactions of Cp*(CO) ₂W(NCMe)Me with Ph₂HGeCî - CR (R = SiMe₃, CMe₃). X-ray crystal analysis of 7a revealed significantly increased germylene-tungsten and decreased germylene-acetylide interactions in comparison to the corresponding interactions in the previously reported acetylide-silylene complex Cp*(CO)₂W(SiPh₂)(CCSiMe₃) (1). Complexes 7a,b reacted with acetone to give the six-membered cyclic vinylidene complexes Cp*(CO)₂W=C=C(R)CMe₂OGePh₂ (8a, R = SiMe₃; 8b, R = CMe₃) by acetone insertion reaction, similar to the case of 1 affording Cp*(CO)₂W=C=C(SiMe ₃)CMe₂OSiPh₂ (2). In the presence of 4-(dimethylamino)pyridine (DMAP), complexes 8a,b gave trans- and cis-DMAP-stabilized germylene acetylide complexes Cp*(CO) ₂W(GePh₂·DMAP)(CCR) (trans- and cis-9a, R = SiMe₃; trans- and cis-9b, R = CMe₃) and acetone, showing a reactivity different from that of the silicon analogue 2. Complexes cis-9a,b were isolated as crystals from the reaction of 7a,b with DMAP and formed mixtures with trans-9a,b in solutions, respectively. A mixture of cis- and trans-9a reacted with acetone to form an equilibrium mixture with 8a and DMAP. The reactivity of 7a,b toward Me₃COH was also investigated to reveal the formation of the vinylidene complexes Cp*(CO)₂W{GePh ₂(OCMe₃)}=C=CHR (10a, R = SiMe₃; 10b, R = CMe₃); 10a is equilibrated with 7a and Me₃COH, whereas 10b is further converted to the carbyne complex Cp*(CO)₂Wî - CCH(CMe₃){GePh₂(OCMe₃)} (11).