(dcpe)Pt(ECp*)2l (E = Al, Ga): Synthesis, structure, and bonding situation of the first aluminum(I) and gallium(I) complexes of phosphine-substituted transition metal centers

Herein we describe the first phosphine-substituted transition metal complexes with terminal coordinated Cp*E ligands (E = Al, Ga; Cp*= pentamethylcyclopentadienyl). The reaction of [(dcpe)Pt(H)(CH2-Bu)] (dcpe = bis(dicyclohexylphosphino)ethane) with Cp*E yields the tetrahedrally coordinated complexes [(dcpe)Pt(A!Cp*)2] (1) and [(dcpe)Pt(GaCp*)2l (2), respectively. Quantum-chemical DFT calculations on the model complexes [(dhpe)Pt(AlCp)2] (IM) and t(dhpe)Pt(GaCp)2] (2M; dhpe = diphosphinoethane) verify rather weak Ft-E bonds for both complexes.'A comparison with the complexes [M(ER)4] and [(CO)rtMER] shows that Cp*E represents a moderate a-donor/7r-acceptor and that the bond strength is strongly influenced by the ancillary ligands at the transition metal center; in particular, (CO)nM fragments give more polar bonds than phosphine-substituted metal centers such as L2Pt.