[(dcpe)Pt(ECp*)₂] (E = Al, Ga): Synthesis, Structure, and Bonding Situation of the First Aluminum(I) and Gallium(I) Complexes of Phosphine-Substituted Transition Metal Centers

Abstract

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)(CH2t-Bu)] (dcpe = bis(dicyclohexylphosphino)ethane) with Cp*E yields the tetrahedrally coordinated complexes [(dcpe)Pt(AlCp*)2] (1) and [(dcpe)Pt(GaCp*)2] (2), respectively. Quantum-chemical DFT calculations on the model complexes [(dhpe)Pt(AlCp)2] (1M) and [(dhpe)Pt(GaCp)2] (2M; dhpe = diphosphinoethane) verify rather weak Pt−E bonds for both complexes. A comparison with the complexes [M(ER)4] and [(CO)nM−ER] shows that Cp*E represents a moderate σ-donor/π-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.