Carbon-13 NMR spectra of monosubstituted tungsten carbonyl complexes. NMR trans influence in octahedral tungsten (0) compounds

Abstract

l3C NMR data and CO stretching force constants of 23 anionic and neutral tungsten pentacarbonyl complexes, W(CO)sL, are compiled. Changes of the 13C chemical shift of the carbonyl groups are shown to arise mainly from the [2M + ß* (? ß] term of the paramagnetic shift contribution. The correlation between 5(I3C) and &(CO) is good even if the ligands L span a wide range in terms of donor/acceptor properties. Strong, single-faced -acceptor ligands L, however, give rise to an additional downfield shift of the 13C resonance of the CO group trans to L. This is explained as being a result of the breakdown of the cylindrical symmetry of the -bonding system within the L-W-C-0 fragment. On the basis of V(183W-13C) of the carbonyl group trans to L, the following trans-influence series of ligands L toward tungsten(O) is established: Ph2C > CO > olefins > CN-, P(OR)3, PR3 > H", CHf, NCS", 0C(0)R", py > RNH2, RCN, SC(S)R", AsR3 > SbR3, SH" > Cl" > Br" > I". A comparison between this trans-influence series and those for square-planar Rh(I) and Pt(II) complexes reveals the importance of metal-carbon bonding in octahedral tungsten carbonyl complexes as a mechanism to strengthen the interaction.

Synthesis and structure of novel triphenylarsine-substituted tungsten(0) Fischer carbene complexes

“…This trend is unexpected, as one would expect the carbonyl stretching frequencies for the complexes containing weaker π-acceptor ligands (AsPh 3 ) to have lower values compared to their phosphine analogues. This observation, however, was also reported for [EPh 3 (CO) 5 W] (E = P, As) [32] and cis-[EPh 3 (CO) 4 WC(OMe)(Me)] (E = P, As) [3], see Table 2. Results in Table 2 show that the Rgroups and identity of E in ER 3 (E = P, As; R = alkyl, aryl or OPh) does not have a significant influence on the position of the A …”

“…This trend is supported by literature reports for the structures of [W(CO) 5 (EPh 3 )], E = P and As [35], where W-E bond length increased with an increase in donor atom size (P < As). The W-C3 bond trans to CO, PPh 3 or AsPh 3 , decreases in length as expected from the trans influence found for ligands in tungsten(0) carbonyl complexes: (largest trans-influence, longest W-C3 trans bond) carbonyl > phosphine > arsine [32,35]. By considering d(W-C1) of the novel complexes as well as literature data [12], the trans-influence trend for the ligands of this series of tetracarbonyl tungsten(0) complexes can be extended to read as follows: carbonyl > carbene > PPh 3 > AsPh 3 .…”

Electrochemical behaviour and structure of novel phosphine- and phosphite-substituted tungsten(0) Fischer carbene complexes

“…are larger than for trans complexes (~205 Hz) [55]. On the 31 P spectra of 5-8, two peaks were seen in each case, confirming the mer arrangement of ligands for phosphorous atoms in non-equivalent positions.…”

Fac and mer dppe-substituted Fischer carbene complexes of chromium: X-ray, DFT and electrochemical study

“…Also, downfield shifts of carbonyls are indicative of increased metal π-bonding [36], as would be expected for a greater degree of carbonyl substitution. The carbene carbon resonances of the aminocarbene complexes 3 and 4 show the characteristic upfield shift [37-39 of 40-60 ppm compared to the ethoxycarbene analogues.…”