6  Nitrogen, phosphorus, arsenic, antimony and bismuth

Abstract

Once again there has been a considerable interest in the chemistry of the group 15 elements. Notable developments include the novel bonding mode of phosphorus ligands discovered by Werner 1 and the construction of nanomaterials using phosphorus-based dendrimers. 2 NitrogenThe fixation of nitrogen continues to be attracting considerable interest and reviews covering recent advances in this area using transition metals and the interaction of substrates with nitrogenase have been published. 3,4 The structure of the MoFe cluster in nitrogenase, and the mechanism of N 2 reduction by this enzyme have been reinvestigated by DFT in the light of new crystallographic data. 5 The calculations support the assignment of the ''light atom'' at the centre of the metal cluster as being nitrogen. A series of ruthenium complexes with sulfur-and phosphorus-containing ligands have been prepared and their potential as models for nitrogenase has been explored. 6,7 A complementary theoretical study into the activation of terminallybound dinitrogen in dinuclear Fe(II) and Ru(II) complexes has also appeared. 8 A comprehensive theoretical study into the reductive cleavage of the NLN bond in the cluster [(g 5 -C 5 H 5 ) 2 Mo 2 (m-SMe) 3 (m-g 1 :g 1 -HNLNPh)] + has shown that the Mo-Mo d-orbital plays a crucial role in this cleavage. 9 An extremely thorough structural and mechanistic study into the cleavage of a range of nitrogen-nitrogen double bonds in tungsten alkoxide complexes has been published. 10 Reduction of the Ti(III) precursor (g 5 -C 5 H 3 -1-3-{SiMe 3 } 2 ) 2 TiCl with sodium amalgam under one atmosphere of N 2 gives the paramagnetic dimeric dinitrogen complex [(g 5 -C 5 H 3 -1-3-{SiMe 3 } 2 ) 2 Ti] 2 (m 2 -g 1 ,g 1 -N 2 )], 1. 11 Reaction of 1 with organic azides RN 3 (R = SiMe 3 , Mes) gives N 2 and imido complexes [(g 5 -C 5 H 3 -1-3-{SiMe 3 } 2 ) 2 Ti(LNR)]. The mechanism of the reaction of the dinitrogen unit in (g 5 -C 5 Me 4 H) 2 Zr) 2 (m-g 2 :g 2 -N 2 ) has been probed by an elegant theoretical and deuterium labelling study and indicates the importance of a 1,2-addition process. 12 The dinitrogen in the zirconium complex ([P 2 N 2 ]Zr) 2 (m-g 2 :g 2 -N 2 ) has been shown to undergo C-N bond forming reactions with terminal aryl alkynes RCMCH to give 2.