A Phosphine-Coordinated Boron-Centered Gomberg-Type Radical.

The P-coordinated boryl radical [Ph2P(naphthyl)BMes]˙ (Mes=mesityl) was prepared by (electro)chemical reduction of the corresponding borenium salt or bromoborane. Electron paramagnetic resonance (EPR) analysis in solution and DFT calculations indicate large spin density on boron (60-70%) and strong P-B interactions (P→B σ donation and B→P negative hyperconjugation). The radical is persistent in solution and participates in a Gomberg-type dimerization process. The associated quinoid-type dimer has been characterized by single-crystal X-ray diffraction.

Synthesis and Coordination Chemistry of Iminophosphanes.

Iminophosphanes are a new group of 1,3-P,N-ligands, readily obtainable from secondary phosphanes and nitrilium ions, having a tunable N-donor site by means of varying the imine substituents. These ligands give, in high yields, monodentate gold complexes and bidentate rhodium and iridium complexes. Crystal structures are reported for both the ligands and the complexes.

Facile synthesis of phosphaamidines and phosphaamidinates using nitrilium ions as an imine synthon.

Readily accessible nitrilium triflates are convenient imine building blocks for the expedient synthesis of a novel class of 1,3-P,N ligands as demonstrated for the reaction with primary phosphanes. This procedure allows variation of all substituents. X-ray crystal structures are reported for nitrilium ions, phosphaamidines, and three phosphaamidinate complexes. The lithium phosphaamidinate is N coordinated and its reaction with [AuCl(tht)] (tht = tetrahydrothiophene) gives a unique P-bridged gold trimer, while a P,N-bidentate complex results from [{RhCl(cod)}2]. The nitrilium ion methodology allows extension of the 1,3-P,N motive to bis(imino)phosphanes, which are the neutral phosphorus analogues of the valuable ß-diketiminate ligand.

Fischer-type gold(I) carbene complexes stabilized by aurophilic interactions.

The synthesis and structure of rare acyclic alkoxy- and aminocarbene complexes of gold(i) are reported, including a novel ferrocenophane dinuclear biscarbene complex. X-Ray diffraction analyses and DFT calculations reveal that these complexes are stabilized by genuine aurophilic interactions.

Isolation of a C5-deprotonated imidazolium, a crystalline "abnormal" N-heterocyclic carbene.

The discovery two decades ago of metal-free stable carbenes, especially imidazol-2-ylidenes [N-heterocyclic carbenes (NHCs)], has led to numerous breakthroughs in organic and organometallic catalysis. More recently, a small range of complexes has been prepared in which alternative NHC isomers, namely imidazol-5-ylidenes (also termed abnormal NHCs or aNHCs, because the carbene center is no longer located between the two nitrogens), coordinate to a transition metal. Here we report the synthesis of a metal-free aNHC that is stable at room temperature, both in the solid state and in solution. Calculations show that the aNHC is more basic than its normal NHC isomer. Because the substituent at the carbon next to the carbene center is a nonbulky phenyl group, a variety of substitution patterns should be tolerated without precluding the isolation of the corresponding aNHC.