Bidentate phosphine

Another unique synthetic methodology for the carbene phosphine bidentate ligand is the utilization of destabilized C-amino phosphorus ylides 25 as carbene source [66]. Due to the electrostatic repulsion between the two lone pairs on the nitrogen and on the ylidic carbon, the yUdic bond is very labile. Thus, these C-amino phosphorus ylides readily act as 1,6-bidentate ligand precursors by insertion of the metal fragment between the phosphine and carbene centers. 

Scheme 8.9 Formation of a phosphite-phosphine bidentate ligand by simply mixing the porphyrin-functionalized phosphite and the 3-pyridyldiphenylphosphine ligand in the presence of a metal precursor.

Trans-bromo structures are also found in the similar ditertiary phosphine bidentate complex [MnBr2(dmpe)2] (dmpe = l,2-bis(dimethylphosphino)ethane) 28 the Mn—P bond length in this compound (2.655 A) being comparable with that found in [MnCl2(diphos)2] (2.625 A). The reaction of [MnBr2(dmpe)] with LiAlH4 yields a Mn1 compound of stoichiometry Mn(AlH4)(dmpe)2 (Section 41.2.4). 

The coordination chemistry of diphosphine and diarsine ligands has been intensively investigated in recent years.i Very much less work has been carried out on the corresponding mixed ligands, the intermediate arsine-phosphine bidentates, owing to a considerable extent to the lack, until recently, of suitable synthetic routes to such ligands. Two routes are now available the nucleophilic substitution of organohalogen compounds, two examples of which... 

A DMPE adduct of U(BH3CH3)3 has been described. It contains two molecules of phosphine per uranium atom. The complex is tetragonal, space group P43 2i2, Z = 4, with a = 1129.7 and b = 2303 pm. The H3BCH3 units are tridentate and the phosphines bidentate. The stereochemistry around the uranium is effectively a pentagonal bipyramid. 

Cobalt(—I) complexes arsenic ligands, 769 bipyridyl, 691 cyanides, 646 phenanthroline, 691 phosphines bidentate, 728 monodentate, 718 multidentate, 738 tridentate, 738 phosphinites, 747 phosphites, 747 phosphonites, 747 terpyridyl, 691 Cobalt(O) Complexes arsenic ligands, 769 bipyridyl, 691 carbon disulfide, 646 cyanides, 646 phenanthroline, 691 phosphines, 718 bidentate, 728 multidentate, 738 tridentate, 738... 

Partial or complete displacement of the coordinated acetonitrile ligands may be achieved with monodentate ligands (e.g., phosphines ), bidentate ligands (e.g., dienes), or tridentate ligands, providing a convenient entry to a range of (i -pentamethylcyclopentadienyl)rhodium and -iridium complexes. 

Various otiier qtproaches have been applied in changing flie Grubbs catalysts, such as the introduction of election-withdrawing phosphines, " bidentate Schiff bases, piridinyl-alcoholate ligands, pyridines (with formation of bis(py-ridine) complex 3), pyridinecarboxylate," different halides," " alkoxides,"" phenoxides," " and substituted acetic acid groiqis." IndenyUdene has been successfully introduced as a substitute for benzylidene. Furthermore, the benzylidene has been successfully altered by Piers et al. through introduction of a phosphonium salt which created a highly active and stable 14-electron initiator. " ... 

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