Group 10–group 14 metal complexes [E–TM]IV: the role of the group 14 site as an L, X and Z-type ligand

Abstract

A series of new complexes of a general motif [R₂E(μ-N,S)₂TM–L] (E: metalloid group 14 element; TM: group 10 metal; R: Cl, Ph, pyS, OH, (N,N,O)-chelating ligands; N,S: 1-methylimidazole-2-thiolate (methimazolyl, mt⁻), pyridine-2-thiolate (pyS⁻); L: PPh₃, PCy₃, pyS) was synthesised and characterised by single-crystal X-ray diffraction, multi-nuclear NMR spectroscopy (¹H, ¹³C, ³¹P, ¹¹⁹Sn), ¹¹⁹Sn Mössbauer spectroscopy and quantum chemical calculations. The E–TM bonding situation in these compounds can be described with various resonance structures which comprise E(II)→TM(II), E(III)–TM(I) and E(IV)←TM(0) features. Thus, in these complexes the atoms of the group 14 based ligand sites reveal L-, X- and Z-type ligand characteristics. A systematic comparison between structural and spectroscopic parameters as well as the results from NLMO analyses of structurally related compounds provided information about the differences in the E–TM bonding situation upon alteration of the metal atoms or ligand patterns. Under investigation are the structurally related compounds [Cl₂Sn(μ-pyS)₂TM–PPh₃] (1: TM = Pd; 2: TM = Ni; 3: TM = Pt), [Cl₂Ge(μ-pyS)₂Pd–PPh₃] (4) and, for in silico analysis, [Cl₂Si(μ-pyS)₂Pd–PPh₃] (5), which indicate a pronounced shift of the E–TM bond electron pair towards TM for TM = Pt. Further complexes serve as representatives of these compounds with different bridging ligands {[Cl₂Sn(μ-mt)₂Pd–PPh₃] (8)}, different trans-E–TM-bound ligands {[Cl₂Sn(μ-pyS)₂Pd–PCy₃] (9), [Cl₂Sn(μ-pyS)₂Pd]₄ (10)} and with different substituents at Sn (including penta- and hexacoordinated tin compounds), i.e., [R₂Sn(μ-pyS)₂Pd–PPh₃] with R = Ph (6) and pyS (7), [(O,N,N)Sn(μ-pyS)₂Pd–PPh₃] (11) and (12) having two different (O,N,N) tridentate ligands, and [(μ-OH)ClSn(μ-pyS)₂Pd–PPh₃]₂ (13). The latter series indicates a shift of the E–TM (= Sn–Pd) bond electron pair towards Pd upon transition from penta- to hexacoordinated tin compounds.