Multiple metal-carbon bonds. 10. Thermally stable tantalum alkylidyne complexes and the crystal structure of Ta(.eta.5-C5Me5)(CPh)(PMe3)2Cl

Abstract

range was 4 kbar. The results, shown in Figure 1, may be summarized by the statement that the activation volume for the concerted shift (I) equals -30 ± 5 cm3/mol and that for the stepwise reaction (II) is +10 ± 2 cm3/mol. These observations clearly confirm that this activation parameter provides a criterion for concertedness in sigmatropic shifts as well as for cycloadditions.Acknowledgment. The National Science Foundation generously supported this investigation. References and Notes(1) Paper 52 in the Series "Kinetics of Reactions in Solutions under Pressure".(2) Summarized in W.

New bonding modes of carbon and heavier group 14 atoms Si–Pb

“…15b) 56 Molecules with a TMQCR 2 double bond and TMRCR triple bond were isolated much later. [57][58][59][60][61] The chemical reactivity of the compounds which possess metal-carbon double and triple bonds suggests that two classes of carbene and carbyne complexes can be distinguished which exhibit different reactivities. The metal-ligand bonding in Fischer-type carbene and carbyne complexes 57,58 is best described in terms of donor-acceptor bonding using the Dewar-Chatt-Duncanson (DCD) model 62 between closed-shell fragments while the bonding in Schrock carbenes and carbynes 60,61 should be considered as electronsharing interactions between triplet (for carbenes) and quartet (for carbynes) fragments (Fig.…”

Benzylidyne Bridges from Diphenylacetylene and a Methylidyne Bridge from Methylmagnesium Chloride

“…A similar experiment with potassium graphite as a reducing agent instead of trisodium heptaantimonide afforded a slightly lower yield of 3 (60%), and with sodium amalgam a 40% yield was obtained. 13 C NMR spectra of the crude product mixtures show the signals of 3 as the main product and of 1,3,5-tri(tert-butyl)cyclopentadiene as a significant byproduct. While sodium heptaantimonide or potassium graphite produced just these two compounds in approximately equimolar amounts, the reduction with sodium amalgam produced other side products as well, which could not be assigned.…”

Insights into the nature of ME bonds in [(PMe3)4ME(Mes)]+ (M = Mo, W) and [(PMe3)5WE(Mes)]+: a dispersion-corrected DFT study

“…Aer the landmark preparation of the rst "Fischer-type" carbyne complex [Br(CO) 4 W(CMe)] in 1973, 1 and "Schrock type" carbyne complex [CpCl(PMe 3 ) 2 Ta(CPh)] in 1978, 2 the chemistry of transition metal-carbyne complexes has attracted much attention in synthetic and theoretical chemical research. [3][4][5][6][7][8][9][10] On the other hand, the chemical community faces many challenges in the synthesis of complexes containing multiply bonded heavier main-group elements, [11][12][13] and therefore the existence of carbyne analogues of the heavier group 14 elements (E ¼ Si-Pb) could not be unambiguously conrmed until the mid-1990s.…”

“…[3][4][5][6][7][8][9][10] On the other hand, the chemical community faces many challenges in the synthesis of complexes containing multiply bonded heavier main-group elements, [11][12][13] and therefore the existence of carbyne analogues of the heavier group 14 elements (E ¼ Si-Pb) could not be unambiguously conrmed until the mid-1990s. Power and co-workers reported the synthesis and crystal structures of the rst stable complexes containing a M^Ge bond [(h 5 -C 5 H 5 )(CO) 2 M^GeR] (M ¼ Cr, Mo, W; R ¼ C 6 H 3 -2,6-Mes 2 , C 6 H 3 -2,6-Trip 2 ). 14,15 Aerwards, a series of molybdenum and tungsten complexes containing triply bonded Si-Pb atoms were structurally characterized and their reactivity was studied by Filippou et al and others.…”