Dicarbonyl complex

Bis(l-methylimidazol-2-yl)methane and -ketone with the dimer [Rh(CO)2Cl]2 in the presence of sodium tetraphenylborate give the dicarbonyl complexes 68 (X CHj, CO L = CO) where the carbonyl ligands may easily be substituted by the triphenyl phosphine ligands to yield 68 (X = CH, CO L = PPh ) (99JOM(588)69). The bis(l-methylbenzimidazol-2-yl)methane analogs of 68 (X=CH2 L=C0, PPhj) can be prepared similarly. 

A single example of a rr-alkyl molybdenum complex was serendipitously prepared from a solution of the very light-sensitive dicarbonyl complex Mo(TPP)(CO)2. 

Frenking s group showed that the Group 11 isocyanides M—NC (M = Cu, Ag and Au) are less well bound compared with the corresponding cyanides M—CN [276]. They also studied CO coordination on Cu, Ag+ and Au with Au(CO)2 being the most stable of all Group 11 dicarbonyl complexes [281]. Vaara et al. demonstrated the importance of relativistic effects in the 13-C NMR nuclear shielding constant in... 

Preparation of Bis(p-indenyl)dicarbonyl Complexes of Titanium and Zirconium... 

Recently an ansa-titanocene dicarbonyl complex containing a siloxy bridge has been reported by Curtis et al. (78). The reaction sequence is shown below. 

Reduction of (Me4Si20)(i -C5H4)2TiCl2 with amalgamated aluminum in the presence of 1 atm of CO led to the corresponding dicarbonyl complex 38 in 80% yield. 

Two other functionally substituted 17-cyclopentadienyl titanium dicarbonyl complexes prepared by Rausch and co-workers include the vinyl Cp compound (i7-C5H4CH=CH2)CpTi(CO)2 (81) and the carbomethoxy Cp compound (rj-C5H4C02Me)CpTi(C0)2 (82). Both were synthesized via the aluminum-induced reductive carbonylation of the corresponding dichloride derivatives. 

All the group 4B metallocene dicarbonyl complexes exhibit two strong metal carbonyl stretching frequencies (Ax and Bf) with the exception of bis(i7-indenyl)dicarbonyltitanium (34) and bis(i7-tetrahydroindenyl)dicar-bonyltitanium they exhibit three frequencies due to splitting of the Bt... 

In none of the cases discussed above is molecular hydrogen involved. The first report of the stoichiometric reduction of coordinated carbon monoxide by molecular hydrogen is that published by Bercaw et al. (35, 36). They reported that mononuclear carbonyl and hydride complexes of bis(pentamethylcyclopentadienyl)zirconium are capable of promoting stoichiometric H2 reduction of CO to methoxide under mild conditions. Thus, treatment of the dicarbonyl complex (rj5-C5Me5)2Zr(CO)2 with... 

The reduction to methoxy-hydrido species (7) is thought to proceed via loss of CO from the dicarbonyl complex followed by addition of hydrogen to give the dihydrido carbonyl species (9). The next step suggested (37) is hydride transfer to the carbonyl carbon to give a formyl species in which both the carbonyl carbon and the carbonyl oxygen coordinate to the metal center, i.e., 10 ... 

Furthermore, the reaction of [Fe(CO)(dppe)H2 Si(OEt)3 ] (B, Figure 57) with Me3PbCl led to the dppe-substituted sily 1-plum by 1-dihydrido complex Fe(CO)(dppe)H2 (PbMe3)[Si(OEt)3] (Figure 57). The dihydride complex is less stable than the dicarbonyl complex and tends to fast decomposition at — 25 °C, especially in polar solvents. 

When neat Mel was used in the reaction with [Rh(CO)2l2], a very small peak was initially identified by IR, which would be consistent with [RhMe(CO)2l3] [31, 32]. Further careful analysis of the IR spectra showed a second peak associated with this species, which would be expected for a cis-dicarbonyl complex. Using and C-Mel, NMR measurements showed the presence of Me and CO resonances which are also consistent with the presence of [RhMe(CO)2l3] . Taken together, the IR and NMR data showed the complex to be the fac, cis isomer. 

Jiang S, Agoston GE, Chen T, Cabal M-P, Turns E (1995) BF3 Et20-promoted allylation reactions of allyl(cyclopentadienyl)iron(II) dicarbonyl complexes with carbonyl compounds. Organometallics 14 4697 -709... 

The cis dicarbonyl intermediate 23 could not be isolated, although it was longer lived when cp = cp [57] than when cp = cp. The cis trans isomerization of the dicarbonyl complex is catalyzed by CO, presumably via an unstable CO-bridged intermediate, which would decay to the tram isomer and carbon monoxide (Sch. 15) [56]. 

The chiral complex 2 also requires the use of strong bases to achieve deprotonation no exchange is observed upon treatment with sodium hydroxide-rf/water-lithium diisopropylamide to generate the enolate 7, which under-... 

The achiral dicarbonyl complex 1 has been shown to undergo facile 1,4-addition of amines and thiols to generate the elaborated acyl complexes 2. The more nucleophilic sulfur atom of 2-mercaptoethanol selectively adds to such complexes45. 

Mo(S2CNEt2)2(CO)L2] (L = PMe2Ph or PMePh2 = dppe) have also been synthesized.62 These monocarbonyl compounds are notable for their very low value of v(CO) (1760-1735 cm"1) implying a very electron-rich metal centre in these complexes.62 They transform readily into the dicarbonyl complexes with CO. 

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