Synthesis, structure and bonding situation of [(dcpe)Pt(InCp*)₂] and {((dcpe)Pt[GaC(SiMe₃)₃]₂} - Two novel examples of platinum complexes of low valent group 13 metal species

In analogy to the corresponding Cp*Al- and Cp*Ga-compounds two further bis(phosphine)platinum complexes [(dcpe)Pt(InCp*)₂] (1(In)) and {((dcpe)Pt[GaC(SiMe₃)₃]₂} (2(Ga)) containing monovalent Group 13 metal species as ligands are accessible by thermal activation of [(dcpe)Pt(H)(CH₂t-Bu)] (dcpe = bis(dicyclohexylphosphino)ethane) followed by the reaction with 2 equiv. of InCp* (Cp* = pentamethylcyclopentadienyl) or GaC(SiMe₃)₃. The crystal structure analysis reveals a distorted tetrahedral coordination of the platinum center for both compounds. The Pt-In distances in 1(In) amount to 2.569(1) and 2.556(1) Å. The Pt-Ga distances in 2(Ga) are exceptionally short and amount to 2.315(1) and 2.318(1) Å. Comparative theoretical investigations have been performed on this type of complexes and allow a deeper insight in the bonding situation. The NBO analysis reveals a significantly larger Pt → Ga π-back-donation for the model compound {(dhpe)Pt[GaC(SiH₃)₃]₂} (2M(Ga)) (0.44 e; dhpe = 1,2-diphosphinoethane) in comparison with the related model compound [(dhpe)Pt(GaCP)₂] (1M(Ga)) (0.29 e) bearing a strong π-donating organic ligand at the Ga center. A similar trend is observed for the Pt-Ga bond dissociation energies (D_e= 33.0 kcal mol^-1 for 2M(Ga), D_e = 18.3 kcal mol^-1 for 1M(Ga)). For the model compound [(dhpe)Pt(InCp)₂] (1M(In)) a value of D_e= 19.1 kcal mol^-1 has been calculated.