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

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.