Phosphorus donors, protonated

Among other new monophosphines prepared by this route are some involving an additional, non-phosphorus donor atom or group. Included among these are the proton-sponge-functionalised phosphines (11), complexes of which are readily studied by electrospray-MS techniques, a series of ortAo-sulfonyl- and ortto-sulfonamido-arylphosphines, e.g., (12), the ort/jo-phosphazenylarylphosphines (13), and the phosphino(boranyl)thiaxanthene (14). ... 

Towards a simple Lewis base, for example the proton, phosphine is a poorer electron donor than ammonia, the larger phosphorus atom being less able to form a stable covalent bond with the acceptor atom or molecule. Phosphine is, therefore, a much weaker base than ammonia and there is no series of phosphonium salts corresponding to the ammonium salts but phosphonium halides. PH4X (X = Cl, Br, I) can be prepared by the direct combination of phosphine with the appropriate hydrogen halide. These compounds are much more easily dissociated than ammonium halides, the most stable being the iodide, but even this dissociates at 333 K PH4I = PH3 -t- HI... 

Besides the thiocyanates, just mentioned, other 5-donor complexes which are of interest are the dialkyl sulfides, [MCl3(SR2)3], produced by the action of SR2 on ethanolic RhCl3 or on [IrClg] ". Phosphorus and arsenic compounds are obtained in similar fashion, and the best known are the yellow to orange complexes, [ML3X3], (M = Rh, Ir X = Cl, Br, I L = trialkyl or triaryl phosphine or arsine). These compounds may exist as either mer or fac isomers, and these are normally distinguished by their proton nmr spectra (a distinction previously made by the measurement of dipole moments). An especially... 

As well as phosphorus ligands, heterocyclic carbenes ligands 10 have proven to be interesting donor ligands for stabilization of transition metal complexes (especially palladium) in ionic liquids. The imidazolium cation is usually presumed to be a simple inert component of the solvent system. However, the proton on the carbon atom at position 2 in the imidazolium is acidic and this carbon atom can be depro-tonated by, for example, basic ligands of the metal complex, to form carbenes (Scheme 5.3-2). 

Phosphine, PH3, is a pyramidal molecule that has an unshared pair of electrons on the phosphorus atom. Therefore, it can function as both a proton acceptor (Pro ns ted base) or an electron pair donor (Lewis base). For the moment, it is the ability to accept protons that will be considered. When ammonia is dissolved in water, the equilibrium... 

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