Coordination chemistry of cis,cis and trans,trans1,1′-[1,2-phenylenebis(methylene)]bis(2,2,3,4,4-pentamethylphosphetane)

Abstract

The cis,cis (5) and trans,trans (9) forms of the bidentate ligand 1,1′-[1,2-phenylenebis(methylene)]bis(2,2,3,4,4-pentamethylphosphetane) have been prepared from common precursors using two separate synthetic routes. The cis,cis isomer is attained selectively through the direct reaction of two mol equivalents of 2,2,3,4,4-pentamethylphosphetane with α,α′-dibromo-o-xylene in acetone. Protection of the 2,2,3,4,4-pentamethylphosphetane with BH₃ and conversion to the lithium phosphido-borane prior to adding the α,α′-dihalo-o-xylene leads to the isolation of the trans,trans isomer of 1,1′-[1,2-phenylenebis(methylene)]bis(2,2,3,4,4-pentamethylphosphetane). Both isomers have been fully characterised by spectroscopic and, in the case of the all-cis isomer, single-crystal X-ray methods. The two isomers have been coordinated to Mo(0) to give complexes of the type cis-Mo(CO)₄(L). The solid state structures of cis-Mo(CO)₄(5), 10, and cis-Mo(CO)₄(9), 12, have been determined by single-crystal X-ray methods and reveal significant differences between the two forms, most notably in the chelate bite angle which is 100.68(18)° in 10 compared to 88.12(2)° in 12. Ligand 5 has also been coordinated to Pd(II) and Pd(0) and the structure of the complex Pd(5)Cl₂ (11) determined by single-crystal methods. The solid-state structure of Pd(5)Cl₂ reveals a significant tetrahedral distortion from the normal square planar geometry.