The d⁴/d³redox pairs [MX(CO)(η-RCCR)Tp′]^z(z = 0 and 1): structural consequences of electron transfer and implications for the inverse halide order

Abstract

The d4 halide complexes [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp'] {X=F, Cl, Br or I; R=Me or Ph; M=Mo or W; Tp'=hydrotris(3,5-dimethylpyrazolyl)borate} undergo one-electron oxidation to the d3 monocations [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+, isolable for M=W, R=Me. X-Ray structural studies on the redox pairs [WX(CO)(eta-MeC[triple bond, length as m-dash]CMe)Tp']z (X=Cl and Br, z=0 and 1), the ESR spectra of the cations [WX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+ (X=F, Cl, Br or I; R=Me or Ph), and DFT calculations on [WX(CO)(eta-MeC[triple bond, length as m-dash]CMe)Tp']z (X=F, Cl, Br and I; z=0 and 1) are consistent with electron removal from a HOMO (of the d4 complexes) which is pi-antibonding with respect to the W-X bond, pi-bonding with respect to the W-C(O) bond, and delta-bonding with respect to the W-Calkyne bonds. The dependence of both oxidation potential and nu(CO) for [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp'] shows an inverse halide order which is consistent with an ionic component to the M-X bond; the small size of fluorine and its closeness to the metal centre leads to the highest energy HOMO and the lowest oxidation potential. In the cations [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+ electronegativity effects become more important, leading to a conventional order for Cl, Br and I. However, high M-F pi-donation is still facilitated by the short M-F distance.

The Influence of Stepwise P-Oxidation on the Coordination and Redox Behavior of W–Bisphosalkyne Complex Ligands

“…IR spectroscopy reveals a distinct influence of phosphine oxidation on the electron density at the metal center. Because alkyne and CO ligands share the same d-orbitals, π-back-donation ability to CO depends heavily on the alkyne π-bonding capacity . Therefore, shifts of the CO vibration frequency to higher energies as observed from 1 to 1E (≈15 cm –1 ) can be related to an increased π-Lewis acidity of the alkyne upon P -oxidation.…”

“…This geometry is a common feature for d 4 alkyne carbonyl complexes, which has been explained by optimized π interactions (see Figure S4). Interestingly, W–C alkyne bond lengths indicate a more symmetrical W–alkyne bonding for 1E {Δ­(W1–C1/W1–C2)} = 0.040 Å ( 1 ), 0.021 Å ( 1O ) and 0.014 Å ( 1S ). The detected P–E bond lengths with 1.485(3) Å for E = O and 1.957(1) for E = S match literature values for simple phosphine analogues …”

Facile Synthesis of a Stable Side‐on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation

“…Intramolecular oxidation of W II by the terminal carbeniumc entre could lead to ab iradical or triplet state which is NMR silent. [15,[34][35][36] The existence of at ungsten-based S = 1/2 system was confirmed by an EPR experiment. The Xb and spectrum in solution (see Supporting Information, Figure S1) displayed ani sotropic hyperfine coupling A I = 26 10 À4 cm À1 to 127 I( I = 5/2, 100 %) centreda t< g > = 2.003, while signs for an additional organic radicalw ere missing.…”

“…By substitution of the iodide ligand by cyanidew ea chieved as ubstantial increase of oxidation stability. [35] The exchange was carriedo ut with AgCN in ethyl propionate for 24 hunder reflux conditions. After purification by columnc hromatography and recrystallization, the product 3d was obtained in good yields (Scheme 2).…”

Tuning the potential of redox-active diphosphine ligands based on the alkyne complexes [Tp*W(CO)L{η2-C2(PPh2)2}]

“…Such a dependence is known in the literature as a reverse halide order. 15,16 The pseudo-halides 5 OTf and 5 CN are similar to each other, with the CN-bond giving an additional, weaker IR band at 2110 cm −1 . The cationic complexes 5 Py -OTf and 5 MeCN -OTf show the highest wavenumbers while the CN-stretch of coordinated MeCN is observed at 2276 cm −1 .…”