Phenylcarbene complexes

In 1986 Yamashida et al. found that the reaction of the (morpholino)phenyl-carbene complex 46 with symmetric alkynes 47 gave the morpholinylindene derivatives 48 and 49, as well as the indanones 50 derived from the latter by hydrolysis, in excellent yields (Scheme 9) [54]. This contrasts with the behavior of the corresponding (methoxy)phenylcarbene complex, which solely undergoes the Dotz reaction [55]. This transformation of the amino-substituted complex 46 apparently does not involve a CO insertion, which is an important feature of the Dotz benzannelation. 

X-Ray crystallographic studies of the methylene complex Os(=CH2)Cl(NO)(PPh3)2 (47) and the phenylcarbene complex OsCl2(CO)(=CHPh)(PPh3)2 (59) have been undertaken to fully characterize these compounds. The only other terminal methylene complexes to be crystallographically characterized are (77S-C5H5 )2MeTa=CH2 (94) and... 

C5Me5)(NO)(P(OPh)3)Re=CH2]PF(i (95), while crystal structures of three other phenylcarbene complexes have been reported (96-98). 

Coordination about the osmium in 47 is best regarded as distorted trigonal bipyramidal with axial triphenylphosphine ligands. The distortion is toward a square pyramidal geometry with an apical nitrosyl ligand. Coordination about Os in the six-coordinate phenylcarbene complex is octahedral, as expected. 

In the first, Fe(CO)5 is converted into the carbonyl hydride anion by reductive decarboxylation following initial OH" attack on a carbonyl carbon (55). The carbonyl group is thus oxidized to carbonate in basic medium. The second reaction, (3) (56), is one of E. O. Fischer s celebrated carbene forming reactions (57). Phenyl lithium reacts with Cr(CO)6 leading to an anionic acyl complex. A subsequent alkylation step using Me30+ yields the methoxy-phenylcarbene complex Cr(CO)5(CPh(OMe)). 

The reaction between 1,2-diphenylcyclopropenone and Fischer carbene complexes produced a mixture of cyclobutenones and diphenylacetylene. When a phenylcarbene complex was employed, benzannulation products were produced... 

Reactions of the type of equation (51) have also been the subject of a kinetic investigation. Rate constants in the forward (fei) and reverse direction ( -1) were determined for a number of combinations of R, R, M in acetone at 25°C. The results are summarized in Table 8. A major conclusion drawn from these results is that steric effects are important. In the absence of steric effects one would expect Ki to show the following patterns (i) It should be larger for P(n-Bu)3 than for P(n-OBu)3 because the former is more basic. (2) It should be larger for R = Ph than R = Me because the former is more electron withdrawing. For the methyl carbene complex (R = Me) Ail is indeed larger with P(n-Bu)3 than with P(n-OBu)3 but for the bulkier phenylcarbene complex (R = Ph) the Ki values for the two nucleophiles are comparable or even smaller with P(n-Bu)3 in the case of the chromium complex. This reversal reflects the larger size of P(n-Bu)3 relative to P(n-OBu)3." ... 

The reactivity of the corresponding phenylcarbene complex contrasts with the behavior of the above diphenylcarbene. Thus, the in situ reaction of olefins with the nonisolated pentacarbonylbenzylidenetungsten, obtained by protonation of this ammonium salt derivative, exclusively gives cyclopropanes without any organic metathesis products or inorganic alkylidene derivative (see Tabled) ... 

In marked contrast to the results of Gassman and Schrock, major differences were noted by Casey and co-workers in a series of studies utilizing phenylcarbene-substituted W(0) complexes in reactions with olefins. The H NMR spectra of new phenylcarbene tungsten and iron (69) complexes indicate a substantial positive charge residing on the carbene carbon, and as expected, these complexes readily form ylides on reaction with phosphines ... 

Use of IRMPD to dissociate precursor silanes can initiate rather complex processes. The mechanism presented in equation 116 can explain the formation of both ground-state singlet SiH2 and excited-state singlet 1D Si atoms396. This mechanism is analogous to the phenylcarbene rearrangement397 and has not been found for vibrationally unexcited... 

Thermolysis of the pentacarbonyl chromium compounds 151 affords tet-racarbonyl chelate complexes by loss of a cis CO group,20 in the same fashion that has been found for ortho-alkoxy phenylcarbene complexes181 and similar products.182 The C=C triple bond of alkoxy(l-alkynyl)carbene complexes 1 is more reactive than that of amino(l-alkynyl)carbene complexes. (CO)5Cr = C(NHMe)—C=CPh was shown to add ethanol very slowly to give (CO)sCr = C(NHMe)-CH=C(OEt)Ph in 79% yield.21... 

Transfer of a phenylcarbene species to alkenes with subsequent formation of phenylcyclopropanes is also observed from the iron complex salt dicarbonyl(t7 -cyclopentadienyl)phenylcar-... 

Electrophilic carbene complexes of tungsten or iron smoothly transfer their phenylcarbene ligand to electron rich olefins. Pentacarbonyl(phcny]carbcnc)tungsten(0) (4) is generated in situ by acid treatment of the precursor salt 36, while the cationic iron complex 5 is a stable, isolable compound7-10. 

The complex cw-[(OC)4Mo CNMeCH2CH2NMe 2] has been shown to be catalytically active in methylmethacrylate polymerization, and weakly active in the metathesis of octa-1,7-diene. Reactions of pentacarbonyltungstendi-phenylcarbene with cyclic enol ethers have been studied in a series of papers. ... 

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