Metallkomplexe mit verbrückenden dimethylphosphidoliganden

Insertion, Rearrangement, and Coupling Processes in the Reactions of the Unsaturated Hydride Complex [W2(η5-C5H5)2(H)(μ-PCy2)(CO)2] with Isocyanides

“…The IR spectrum of 3 displays two C–O stretching bands with relative intensities (medium and very strong, in order of decreasing frequency) indicative also of a transoid arrangement of the WCp­(CO) fragments of the molecule, with carbonyls defining an angle somewhat lower than 180° . This might result from increased steric demands of the ligands at the bridging positions, no doubt related with the large size of the Xyl substituent.…”

“…As it is also the case of bridging alkoxycarbyne ligands in related dinuclear complexes of the type [Mo 2 Cp 2 (μ-COR)­(μ-PCy 2 )­(CO) 2 ], the electronic distribution within the coordinated aminocarbyne ligand in 4 is expected to retain some degree of π bonding between the C and N atoms, a circumstance which is usually represented by using an iminium canonical structure ( R2 in Chart ) in addition to the aminocarbyne structure ( R1 ). ,− This in turn implies that rotation around the C–N bond might be somehow restricted. Of course the steric interactions of the R group might also contribute to increasing the corresponding rotation barrier.…”

“…The transformation of a formimidoyl complex into its aminocarbyne isomer is unexpected for several reasons: (a) apparently, there is no precedent for such a transformation, even after attempts to achieve it; (b) aminocarbyne complexes seem to be preferentially formed in the presence of proton-transfer agents, as noted in the Introduction section; and (c) there is at least one precedent for the reverse transformation, but this again takes place in the presence proton-transfer agents. Thus, Werner et al found that the reaction of CNMe with the electron-precise, hydride-bridged cation [Co 2 Cp 2 (μ-PMe 2 ) 2 (μ-H)] + in methanol gave first the adduct [Co 2 Cp 2 (μ-PMe 2 ) 2 (H)­(CNMe)] + , the latter thermally rearranging to the aminocarbyne [Co 2 Cp 2 (μ-PMe 2 ) 2 (μ-CNHMe)] + , which in the presence of methylamine yielded the formimidoyl isomer [Co 2 Cp 2 (μ-PMe 2 ) 2 (μ-HCNMe)] + , thus proving for the first time that formation of formimidoyl ligands by insertion of isocyanides in M–H or M–H–M bonds might occur with μ-aminocarbyne complexes as intermediates . Further experiments with other isocyanides and calculations will have to be done to gain insight on this unexpected transformation, particularly concerning the role that the unsaturated ditungsten center of complex 1 plays on it.…”

Preparation and Protonation of Fe2(pdt)(CNR)6, Electron-Rich Analogues of Fe2(pdt)(CO)6

“…A doublet and quasiquartet appear, respectively, at δ 3.34 and 8.33, with integrated intensity 3:1 and an apparent J HH = 4.8 Hz. Comparable NMR shifts and couplings are observed for the aminocarbyne [Cp 2 Co 2 ­(μ-PMe 2 ) 2 (μ-CN Me ( H ))] + . The low-field portion of the 13 C­{ 1 H} NMR spectrum displays a signal at δ 340 as well as resonances at δ 166, 165, and 164.…”

“…Comparable NMR shifts and couplings are observed for the aminocarbyne [Cp 2 Co 2 (μ-PMe 2 ) 2 (μ-CNMe(H))] + . 33 The lowfield portion of the 13 C{ 1 H} NMR spectrum displays a signal at δ 340 as well as resonances at δ 166, 165, and 164. The 13 C NMR signal at δ 340 is also consistent with a bridging aminocarbyne ligand, 34,35 indicating that protonation occurs at the MeNC ligand.…”