Symmetric and Non-Symmetric Dinuclear Alkenyl-Bridged Carbene Complexes of Chromium and Tungsten

Abstract

Treatment of (CO)5W=C(NMe2)CH=CH−Ar−(OH)(H)C≡CH (1a−b) [a: −Ar− =1,4‐C6H4−; b: −Ar− = 2,5‐C4H2S−] with W(CO)5(THF) in methanol yields the nonsymmetrical bis(alkenylcarbene)‐bridged ditungsten complexes (CO)5W=C(NMe2)CH=CH−Ar−CH=CH(OMe)C=W(CO)5 (3a−b). Similarly, the symmetrical bis(methoxycarbene)ditungsten derivative [(CO)5W=C(OMe)CH=CH−]2(1,4‐C6H4−) (4a) is obtained in a low yield from the precursor (CO)5W=C(OMe)CH=CH−C6H4−(OH)(H)C≡CH (2a). Complexes 3a and 3b undergo aminolysis reactions with diamines such as piperazine and ethylenediamine to produce the corresponding bis[alkenyl(amino)carbene]ditungsten complexes 5a−b and 6a−b. The reaction of 1a with Cr(CO)5(THF) affords the heterobimetallic (W−Cr) bis(carbene) complex (CO)5W=C(NMe2)CH=CH−Ar−CH=CH(OMe)C=Cr(CO)5 (3′a). This complex, as well as the bis(methoxycarbene) derivative 4′a, can also be obtained by treatment of (CO)5W=C(XR)CH=CH−C6H4−CHO [1c: XR = NMe2; 2c: XR = OMe] with (CO)5Cr=C(OMe)CH2−Li+. All the new compounds have been characterized by analytical and spectroscopic methods, and the single‐crystal structures of 3a, 4a−b, and 4′a have been established.

Fischer-Type Carbene Complexes of Tris(1,4-phenylene)amines and Tri(2-furyl)phosphine

“…The 1 H NMR chemical shifts for the protons of the furyl rings with or without carbene substituents and the ethoxycarbene substituents generally remained approximately the same in spite of the number of carbene substituents increasing from one (4) to two (5) to three (6). This was supported by similar values found for the resonances in the 1 H and 13 C NMR spectra for the WC(OEt)Fur-unit 30 and the complexes 4b−6b. The carbene carbon chemical shifts in the 13 C NMR spectra are insensitive on increasing the number of carbene substituents and remain the same.…”

“…39 The 13 C NMR spectra of the compounds reveal that the carbene carbon signals move downfield as the number of carbene substituents on the molecule increase: 1 (a, 332.6; b, 308.6 ppm), 2 (a, 337.9; b, 311.1 ppm), 3 (a, 337.9; b, 312.6 ppm). In the 13 C NMR spectra, metal−carbonyl resonances are metal-sensitive but are insensitive to the number of carbene substituents and give similar δ-values for 1, 2, and 3. The same is true for the vibrational frequencies in the IR spectra of 1, 2, and 3.…”

“…NMR spectra were recorded on Bruker Ultrashield Plus 400 AVANCE 3 and Bruker Ultrashield 300 AVANCE 3 spectrometers using CDCl 3 and C 6 D 6 as solvents at 25°C. The NMR spectra were recorded for 1 H at 400.13 and 300.13 MHz, 13 3 and C 6 D 6 , respectively, δH at 7.2400 and 7.1500 ppm, and δC at 77.000 and 128.000 ppm, and the 31 P NMR spectra were referenced to the deuterated lock solvent which had been referenced to 85% H 3 PO 4 . Infrared spectroscopy was performed on a PerkinElmer Spectrum RXI FT-IR spectrophotometer with a NaCl cell, using hexane as solvent.…”

“…A plausible interpretation involves a furyl metal acylate intermediate (I) being subjected to a nucleophilic displacement reaction by the butyl group of nBuLi. It was assumed that in I Assignments of the furyl ring proton signals in the 1 H NMR spectra were based on the chemical shifts, their patterns and the magnitude of 31 P-coupling constants displayed by a particular ring proton in the 1 H and 13 C NMR spectra. The protons furthest downfield in the 1 H NMR spectra were assigned to the proton in the 5-position of the unsubstituted furan rings.…”

Recent advances in the field of multicarbene and multimetal carbene complexes of the Fischer-type

“…The spacer unit may be a π-conjugated substrate in which case the terminal metal fragments will be in electronic contact with each other via the carbene moiety and through the spacer unit. Biscarbene complexes with heteroarene spacer units have been investigated [63][64][65][66][67][68]. Examples of biscarbene complexes with alternating unsaturated carbon-carbon bonds have been reported [69,70].…”