Coordination Properties of Multidentate Phosphanylborane Ligands in Tungsten Nitrosyl Complexes

Abstract

AbstractThe ambiphilic and small‐bite‐angle diphosphanylborane ligands Ph2PCH(PPh2)CH2B(C8H14) (2) and Ph2PCH2CH[B(C8H14)]PPh2 (3) containing the Lewis acidic 9‐boranorbornyl group B(C8H14) have been prepared in one step by regioselective anti‐Markovnikov hydroborations of 1,1‐bis(diphenylphosphanyl)ethylene and 1,2‐bis(diphenylphosphanyl)ethylene with 9‐borabicyclo[3.3.1]nonane (9‐BBN) under relatively drastic reaction condition. The coordination properties of Ph2PCH2CH2B(C8H14) (1) and the newly prepared 2 and 3 towards the tungsten nitrosyl fragment {WNO}6 have been studied structurally and spectroscopically. Herein, we report the cis and trans tungsten nitrosyl complexes cis‐[W(CO)2(1)2(NO)(Cl)] (cis‐4a), cis‐[W(CO)2(1)2(NO)(H)] (cis‐4b), trans‐[W(CO)2(1)2(NO)(Cl)] (trans‐4a), trans‐[W(CO)2(1)2(NO)(H)] (trans‐4b), cis‐[W(CO)2(2)(NO)(Cl)] (cis‐5a), cis‐[W(CO)2(2)(NO)(H)] (cis‐5b), cis‐[W(CO)2(3)(NO)(Cl)] (cis‐6a), cis‐[W(CO)2(3)(NO)(H)] (cis‐6b), which were readily obtained from straightforward ligand‐substitution reactions of the tungsten carbonyl nitrosyl precursor [W(NO)(CO)4(ClAlCl3)] in tetrahydrofuran. The crystal structures of the tungsten chloride complexes cis‐4a, trans‐4a, and cis‐5a revealed that the trialkyl boron centers are free pendants in the secondary coordination spheres, whereas in the hydride complexes trans‐4b, cis‐5b, and cis‐6b the hydride ligand trans to the nitrosyl ligand is σ coordinated to the tethered B(C8H14) group and form three‐center, two‐electron (3c–2e) W–H–B bonds, which were observed in their crystal structures. The authenticity of the 3c–2e W–H–B bond in the tungsten hydride complex cis‐5b was further checked by a DFT structural optimization and natural bond order (NBO) analysis.