Co , bridged

Structures in which one or more (but not all) rings of an aggregate are lactone rings are named by placing -carbolactone (denoting the —O—CO— bridge) after the names of the structures that... 

When the carbonyl groups are present, the transition state for syn attack is sta-bihzed by interactions between the in-phase combination of the NN lone pairs and the antisymmetric n orbital of the CO-X-CO bridge (100). Although the secondary effect (SOI) operates only during syn approach and contributes added stabilization to this transition state, the primary orbital interaction (see 103) between the HOMO of the cyclohexadiene moiety of 100 and the n orbital of the dienophile (NN, Fig. 16) is differentiated with respect to the direction of attack, i.e., syn or anti, of triazolinedione (NN, Fig. 16). 

The known reactions involving transfer of a C5HSBR ligand are collected in Table VII. Alternative syntheses are available for the bis(borata-benzene)iron complexes 65 and 18 only (55). In the system 7/Ni(CO)4 the main product is Co(CO)2(C5H5BMe) (15), and 66 is obtained as a thermally unstable by-product (47). In solution, 66 adopts a folded, doubly CO-bridged structure with a dihedral angle of 121° for the Ni2(CO)2 moiety (47). 

Does isomerization to form three CO-bridges occur before or after the loss... 

Church and co-workers (77) have obtained time-resolved IR spectra of both Mn(CO)5 and Mn2(CO)9 by flash photolysis of Mn2(CO)I0 in solution. The spectra (Fig. 11) were in close agreement with the spectra of matrix isolated Mn(CO)5 (22) and Mn2(CO)9 (5,106). There was a bridging vc 0 band for Mn2(CO)9 showing that it has a CO-bridged structure in solution as well as in the matrix. Structural information of this type could not have been obtained from uv-vis spectroscopy. Similarly, the IR spectra indicated that Mn(CO)5 had the same C4v structure in solution (77) as in the matrix (22). In solution (77), the yield of Mn2(CO)9 was approximately equal to that of Mn(CO)5. Bearing in mind that one molecule of Mn2(CO),0 produces two molecules of Mn(CO)5 [Eq. (14)], CO loss from Mn2(CO)10 [Eq. (15)], must be the major process at these photolysis wavelengths (37,77). 

It is interesting to note that the photosubstitution intermediate 11 appears to be significantly more selective toward reaction with various two electron donor substrates than is the photofragmentation intermediate 1. One speculative rationalization of this is that the Ru3(C0) intermediate has the opportunity to "delocalize" its unsaturation by having one CO bridge an edge of the metal triangle with concomitant formation of a multiple metal-metal bond. 

Another dinuclear carbonyl which presents interesting problems is ](ri C5H5)Fe(CO) ] 2 Does the photochemistry proceed exclusively through homolytic fission to produce two (13 -05 )Fe-(C0)2 radicals or by other possible routes The discussion of this reaction has involved mechanistic and synthetic studies (77), flash photolysis (78) and low-temperature photolysis (29) - the latter work, in THF or ethyl chloride at -78°C, invokes an intermediate in which the Fe-Fe direct bond is broken but the two halves of the molecule are held together by a CO bridge. Clearly such an intriguing problem merits more detailed investigations. 

For cluster breakdown to occur, therefore, we must consider two stages, (i) The formation of an excited state geometry which contains CO bridges and must satisfy the criteria laid out above, i.e., there must be sufficient CO groups per metal atom within the cluster to produce a saturated unit. This will require an energy Et. (ii) The ejection of the saturated unit, which will require an additional energy E2. 

Similarly, Rh,(CO)12 easily converts to RhgCCO),. Again, E1 is effectively zero since the C3v arrangement has been established in both the solid and solution. The mixed system Fe2Ru(CO)12, which contains CO bridges, undergoes disproportionation more readily than Ru2Fe(CO)12, which does not. 

A123 Onaka, S., Shriver, D. Inorg. Chem. 15, 915 (1976) Raman studies indicate that for first row transition metals v (metal-metal) are above 200 cm-1 for CO bridged and between 190 and 140 cm-1 for unbridged compounds... 

Arrhenius parameters calculated from the data in Tables 1-4 are shown in Table 5. The pre-exponential factors are all within the range expected for uni-molecular decompositions, with the exception of Co2(CO)6C2H2. The low value for its decomposition has been attributed to formation of a CO bridge in the transition state24. 

Starting with Fe3(CO)i2, another trinuclear complex is obtained having two doubly bridging GaR units (Equation (81)).67 The Ga-bridged Fe-Fe bond distances in 72 are 277.85(7) and 276.51(7) pm, while the CO-bridged Fe-Fe bond is shorter at 266.61(8) pm.67... 

Alanes, CO bridging, 28 90, 91 Albite, 33 255 AICI3, 37 168, 172-173 -CuClj, 37 173 -CUSO4 mixture, 37 173 Alcohol carbonylation... 

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]. 

Coordination Geometry Around the Metal Ion in Reported iu-CO Bridged Complexes... 

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