Reactions of cyanoalkenes with a tungsten hydrazido (2–) complex: the X-ray crystal structure of [WBr(dppe)₂{NC(Br)C(CN)C(CN)₂}], a bromotricyanoprop-2-enylideneamino-complex

Organic chemistry of dinitrogen and related ligands. Part 7. N-Vinylation or oxidative replacement of the hydrazido(2–) ligand in reactions of [WX(dppe)2(NNH2)]Y (dppe = Ph2PCH2CH2PPh2, X = F or Br, Y = BF4or Br) with cyanoalkenes. X-Ray crystal structure of [WBr(dppe)2{NC(Br)-C(CN)C(CN)2}]

“…-2 809( 7) 424(4) -1 871 (6) 504( 3) 632( 6) 355(3) 2 475 (6) 676(3) 3 163( 6) 970(3) 4 064 (8) 845(4) 4 3 14 ( 7) 420(4) 3 648 (7) 115(3) 2 730 (6) 244( 3) 1224 (6) 1219( 3) 1975 (7) 1357(3) 1918 (9) 1635(4) 1 051(9)…”

The organic chemistry of dinitrogen

“…We have found, for example, that they readily attack electrophilic alkenes such as 1,1dicyano-2-ethoxyethene to give compounds containing substituted vinyldiazenido(l-) ligands (SchemeVII). 29 The reactions were carried out by addition of a tertiary amine to a solution containing the alkene and hydrazido(2-) complex, so generating the diazenido(l-) complex in situ. On one occasion, however, when tetracyanoethene (TCNE) was used as substrate, a reaction was observed even in the absence of base, though two molecular equivalents of TCNE were required for complete conversion of the hydrazido(2-) complex.…”

“…The product was finally identified crystallographically as a novel complex containing the previously unknown bromotricyanoprop-2-enylideneamino ligand (Scheme VIII). 29 In order to account for this result, we have proposed29 that one molecule of TCNE serves to oxidize the hydrazido(2-) ligand back to N2 (a reaction known to occur with other oxidizing agents8) and that the second TCNE molecule displaces dinitrogen from the complex to give a cationic, 16-electron intermediate containing N-coordinated TCNE. Addition of bromide ion to the coordinated nitrile group then generates the observed, neutral, 18-electron structure (Scheme VIII).…”