CpMo complexes

Few quantitative data are available on the relative nucleophilicities of L toward various alkyl carbonyls. The rates of the reaction of CpMo(CO)3Me with L in toluene (Table II) decrease as a function of the latter reactant P( -Bu)3 > P( -OBu)j > PPhj > P(OPh)j, but the spread is relatively small (<8). The above order is that customarily observed for 8 2 reactions of low-valent transition metal complexes (J, 214). Interestingly, neither CpMo(CO)3Me nor CpFe(CO)2Me reacts with 1 or N, S, and As donor ligands 28, 79). This is in direct contrast to the insertion reactions of MeMn(CO)5 which manifest much less selectivity toward various L (see Section VI,B,C,D for details). 

Rather limited information is available on how the nature of R affects the rate of CO insertion, all other factors being constant. A generalization that ethylmetal complexes react faster than the corresponding methyl carbonyls derives from investigations on four systems RIr(CO)2(AsPh3)Cl2 (92), RMn(CO)5 (51), CpFe(CO)2R (98), and CpMo(CO)jR (80). When R = Et the reactions with CO or P and As donor ligands proceed at least 6 times faster than when R = Me. 

In some instances the decarbonylation can be effected, under mild conditions, by using a stoichiometric amount of a CO-abstracting metal complex. This method has proved to be fruitful for several CpFe(CO)2COR compounds (7, 2, 2a) and for CpMo(CO)2(PPh3)COPh 189) in conjunction with Rh(PPh3)jCl. 

Unlike the parent tricarbonyls, complexes of the type CpMo(CO)2LR do not appear to undergo CO insertion. Attempts at the carbonylation of CpMo(CO)2(PPh3)Me under 78 atm of CO were unsuccessful (17) passing CO through a solution of the dicarbonyl in THF at reflux afforded only some CpMo(CO)jMe (20),... 

The decarbonylation of the perfluoroacyl complexes CpMo(CO)3CORp (Rp = CFj and C3F7) and [CpMo(CO)3]2[CO(CF2)3CO], which are much more stable than their hydrocarbon counterparts, can be effected by heating at 115°-130°C (141). However, an attempted elimination of the acyl CO from CpMo(CO)3COCF3 with Rh(PPh3)3Cl gave only CpMo(CO)2-(PPh3)COCFj (1). 

CpMo(S2C2Ph2)2] at 2.0275, 2.0074 and 1.9936 or from oriented single-crystal for [Cp Mo(dmit)2] at 2.027, 2.012 and 1.992, demonstrate an extensive delocalization of the unpaired electron the dithiolene ligands. The solid state properties of these series of radical complexes will be described below in detail in Sect. 3. 

The Mo(III) d3-d3 complexes [CpMo(dithiolene)]2 are characterized by a single Mo—Mo bond, further stabilized by interaction with the n system of the dithiolene ligands. Indeed, the analogous complexes where the two dithiolene are replaced by four thiolate groups were found to oxidize more easily and salts of the cationic d3-d2 [CpMo(SMe)4MoCp]+ were even isolated and structurally and magnetically characterized [50]. 

Reduction of the metal dimer [CpMo(NO)l2]2 with Na/Hg in the presence of a variety of acyclic dienes generates the (diene)MoCp(NO) complexes in moderate to low isolated yield (equation 8)12,31,89. For the majority of diene ligands, complexes 60 are formed exclusively as the s-trans isomers as evidenced by NMR spectroscopy and single-crystal X-ray diffraction analysis. In comparison, complexation of the 2,3-dimethyl-l,3-butadiene initially gives a separable mixture of the s-trans (60) and s-d.v-complex (61). The s-cis isomer isomerizes to the more thermodynamically stable s-trans isomer in solution (THF, 1/2 = 5 min C6H6, ti/2 = 24 h). 

The distortion is even more severe in the triple-decker complex (CpMo)2As4S where the planar middle deck is closer to an allylic Ass group and a separate AsS group rather than an AS4S ring <90IC798>. 

Table 9 Cyclooctene epoxidation with TBHP/complexes M0X2O2L2 (X = Cl, Me L = Lewis base) 1-3 and CpMo(CO)3Me, CpMo(CO)3Cl, Me5CpMo(CO)3Me in different RTlLs...

Related to this group of complexes are the transition metal half-sandwich dithiolates, almost exclusively with the mnt or tfd ligands, of the type CpMLm(mnt) , where m = 0-2 and n = 1 or 2. Examples7 are the linear CpCo(mnt) and CpCo(tfd) complexes (39) and CpMo(tfd)2 (40). The structure of the tetramethylcyclobutadieneNi(mnt) complex has been reported.54 The synthesis and structure of Rh(cod)(Me-mnt) has also been published.55... 

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