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

Abstract

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 η 6 through one phosphinine [Mo(CO) 3 (η 6 -1)] (2Mo), η 6 through both phosphinines to two metal centers [{M(CO) 3 } 2 (μ-η 6 :η 6 -1)] (3M 2 , M = Cr, Mo), and chelating with η 1 coordination through both phosphines [M(CO) 4 (κ:η 1 :η 1 -1)] (4M, M = Cr, Mo). However, only 3Mo 2 could be isolated analytically pure. Heating species 3Mo 2 in the presence of [Pd(COD)Cl 2 ] removed one CO ligand and generated [{Mo(CO) 2 }(μ-κ:η 1 η 6 -η 6 -1){Mo(CO) 3 }] (5), which is the first crystallized example of a bis(phosphinine) featuring chelating η 1 and η 6 coordination, as well as a metal center bound to two phosphinines with different binding modes. In order to enforce a chelating bis-η 1 binding mode, the Ru complex [Ru(Cp*)(Cl)(κ:η 1 :η 1 -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:η 1 :η 1 -1)] ( 7) afforded the first crystallographically characterized example of a complex with both phosphinine and hydride ligands at the same metal center.

Reactivity Studies of Phosphinines: The Selenation of Diphenyl-Phosphine Substituents and Formation of a Chelating Bis(Phosphinine) Palladium(II) Complex

“…1 H NMR spectroscopy revealed 2 multiplets for the H atoms at the 4-and 5-positions along with 1 resonance for the 3-Me group and 1 SiMe 3 environment in agreement with a plane of symmetry passing through the palladium and the SiMe 2 group. However, the presence of two resonances for the SiMe 2 group indicated that the ligand was not coplanar with the PdCl 2 fragment, as has been seen previously in complexes of this ligand with other metal fragments [58]. We attributed this flexibility to bind to metals out of the plane of the ligand to the high s-character of the phosphinine lone pairs, which render them less directional [11].…”

“…Other related examples are cationic and supported by a β-diketiminate framework [56,57]. The phosphinines 4 [58], 5 [36] and 6 [18] all featured additional P donors, either another phosphinine ring (4) or PPh 2 moieties. They were synthesised by the reaction of diazaphosphinine (3) with alkynes in two sequential steps due to the slower reaction of the intermediate azaphosphinines with alkynes.…”

“…Non-dry solvents were used as received from Fisher Scientific or Goss Scientific (deuterated solvents). Cp 2 TiMe 2 [66], diazaphosphinine [46,47] and the phosphinines 4 [58], 5 [36] and 6 [18] were synthesised as previously described. NMR spectra were obtained using either a Bruker AVIII400 (400 MHz) or an AVIIHD (400 MHz) spectrometer.…”

Synthesis of Phosphinines from CoII-Catalyzed [2+2+2] Cycloaddition Reactions

“…While pyridines belong to the core area of heteroaromatic chemistry, phosphinines (also coined phosphabenzenes) have a much shorter history . However, their molecular properties, e.g., in comparison to pyridines, in homogeneous catalysis and coordination chemistry, , have stirred significant work over recent decades toward their synthesis and functionalization Scheme , top).…”

A ruthenium cis-dihydride with 2-phosphinophosphinine ligands catalyses the acceptorless dehydrogenation of benzyl alcohol

“…46,51 Ruthenium hydrides are implicated in many catalytic reactions, yet the first Ru complex comprising of both a hydride and phosphinine ligand has only been described recently by us. 52 Herein, we describe the first ruthenium phosphinine dihydride complex and compare its catalytic activity to that of classical diphosphine-supported complexes for AD reactions.…”