Unexpected Multiple Coordination Modes in Silyl-Bridged Bis(phosphinine) Complexes

The bis(phosphinine) [bis{3-methyl-6-(trimethylsilyl)phosphinine-2-yl}dimethylsilane] (1) was synthesized and its coordination chemistry explored. Molybdenum and chromium carbonyl complexes were crystallographically characterized featuring 1 bound η6 through one phosphinine [Mo(CO)3(η6-1)] (2Mo), η6 through both phosphinines to two metal centers [{M(CO)3}2(μ-η6:η6-1)] (3M2, M = Cr, Mo), and chelating with η1 coordination through both phosphines [M(CO)4(κ:η1:η1-1)] (4M, M = Cr, Mo). However, only 3Mo2 could be isolated analytically pure. Heating species 3Mo2 in the presence of [Pd(COD)Cl2] removed one CO ligand and generated [{Mo(CO)2}(μ-κ:η1η6-η6-1){Mo(CO)3}] (5), which is the first crystallized example of a bis(phosphinine) featuring chelating η1 and η6 coordination, as well as a metal center bound to two phosphinines with different binding modes. In order to enforce a chelating bis-η1 binding mode, the Ru complex [Ru(Cp*)(Cl)(κ:η1:η1-1)] (6) was prepared, demonstrating that judicious choice of metal fragment can dictate the coordination mode of a bis(phosphinine). Conversion of 6 to the hydride species [Ru(Cp*)(H)(κ:η1:η1-1)] (7) afforded the first crystallographically characterized example of a complex with both phosphinine and hydride ligands at the same metal center.