CpFe CH

Both the alkyl and the acyl have two asymmetric centers the iron and the )3-carbon. Accordingly, each composition exists as a pair of racemic mixtures. When the two diastereomeric racemic mixtures of the acyl are separately subjected to the decarbonylation in Eq. (54), only partial (<50%) epimerization is observed by NMR spectroscopy. This indicates that in the reactive intermediate, presumably three-coordinate CpFe(PPh3)COCH2-CH(Me)Ph, the iron substantially retains its asymmetry, and is therefore not planar. 

CpFe(C0)PPh3(C(0Et)CH3)+ (10) to the ethyl complex 8 plus the a-ethoxyethyl compound CpFe C0)PPh3(CH(0Et)CH3) (63). By using PPhsMe+BHi - in CH2CI2, we obtained the desired selectivity the same a-alkuxyethylidene compound exclusively gave 8 in 78% yield. 

The stannylene Sn[CH(SiMe3)2]2 behaves as a Lewis base in its reactions with [CpFe(CO)2]2 to form Cp2Fe2(CO)3(SnR2). Pyridine, 4-methylpyridine and piperidine form dissociable 1 1 adducts265. 

Complex 9 and [CpFe(o-BPXCO)CH 2C1 ] [o-BP = tri(o-biphenyl)-phosphite] were also prepared by the reaction of HC1 with [CpFe(L)-(CO)CH2OEt] (L = PPh3, o-BP) (47). Alkylation of the two complexes with sodium /crt-butyl acetoacetate and pyrroline cyclohexanone enamine yielded six of the eight possible alkylation products. The two products where L was o-BP and the nucleophile was tort-butyl acetoacetate did not form, presumably because of excessive steric hindrance. The excess of one diastereomer over the other ranged from 10 to 64%. 

Consistent with our analyses above, CpMn(CO)3 is a known 18-electron compound. The 17-electron CpMo(CO)3 fragment is found as a dimer with an M-M single bond (Figure 4.8). In order to be isolobal with CH3, the latter must use one t2g orbital plus one electron in bonding. Seventeen-electron CpFe(CO)2, with an unused, filled t2g set, is also isolobal with CH3 Further, 15-electron CpMo(CO)2 behaves as if it were isolobal with CH as it is found as a dimer with a short Mo-Mo bond attributed to a Mo=Mo triple bond. Hence, two of the t2g orbitals and three electrons must be used in the bonding. The Fe analog, 15-electron CpFe(CO) also forms a multiply bonded dimer which is isolated at low temperatures by photolysis of [CpFe(CO)2]2 in an inert matrix. It now must utilize one orbital from the t2g set to be viewed as isolobal with CH. 

Other investigations have established that complexes containing R groups which can engage in w-bonding with the metal generally appear to be inert to the insertion. Accordingly, CpFe(CO)2R with R = CH=CH2, CH=C=CHa, CH=C=CHMe, C=CMe 124), C(0)Me, and C(0)Ph 13) do not react with neat SO2 at temperatures up to... 

Transition-metal hydrides react with olefins to form (T-bonded derivatives h -CpFeteO H + C F - h5-CpFe(CO)jC2F H PtHfClXPEtj) + CjH, -- P(C2H5)Cl(PEt3)2 RhH(CO)(PPh,)3 + MeCHCH, - PPh, + Rh(MeCH,CH,)(CO)(PPh3),... 

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