Atom carbonylation

When sp hybridised carbon atoms (carbonyl groups, olefinic fragments, aromatic rings) are present in an aliphatic carbon chain they cause a downfield shift of 1-2 ppm when present at They have less than half of this effect when present at Cp... 

Other metallacyclobutane derivatives demonstrate similar two-atom carbonyl insertion reactions, as previously reviewed in CHEC-II(1996) <1996CHEC-II(lb)887>. The insertion of diphenylketene occurs exclusively into the C(sp3)-Ti bond of a-methylenetitanacyclobutane complex 79 to give oxatitanacyclohexane 101 (Equation 31) <1993JOM181>. In contrast, no reaction was observed using carbon dioxide or arylisocyanate at room temperature (see Section 2.12.6.2.4). 

Nonphotolytic carbonylations catalyzed by Co2(CO)8 may also occur. With molecular sieves replacing a base, iodoalkanes containing /1-hydrogen atoms carbonylate to esters (equation 206)410. In adition, either Co2(CO)8 or preformed NaCo(CO)4 are capable of car-bonylating or doubly carbonylating benzyl halides under low CO pressures, depending upon the solvent and base employed406,411. 

Structures of the mononuclear (containing only one metal atom) carbonyls are comparatively simple. As shown in Figure 21.4, nickel tetracarbonyl is tetrahedral, the pentacarbonyls of iron, ruthenium, and osmium are trigonal bipyramidal, and the hexacarbonyls of vanadium, chromium, molybdenum, and tungsten are octahedral. 

With respect to intersystem crossing, it appears that the cutoff between small-molecule behavior and the intermediate case is at six atoms, with formaldehyde totally in the small-molecule category, glyoxal a borderline case depending on excitation energy, and propynal intermediate in class. The five-atom carbonyl ketene unfortunately possesses a unique photochemistry which prevents its use in studies similar to those which have been carried out on formaldehyde and glyoxal. 

Carbonylation is a convenient method for the replacement of the boron atom in boracyclanes with a carbon atom. Carbonylation of 9-boradecalin (2) under 70 atm of CO (50- 150°C) in the presence of ethylene glycol results in a mixture of as- and /ran -2-(9-decalyl)-l,3,2-dioxaboroles... 

Cluster Compounds of Co, Rh, and Ir. In addition to the above-mentioned neutral cluster compounds, there is a large number of anionic carbonyl clusters and metal carbonyl carbides. Carbonyl carbides are formed when the interstice inside the metal cluster is sufficiently large to accommodate the carbon atom. Carbonyl carbides possessing at least four metal atoms are known. The most thoroughly investigated carbides are those of rhodium because they are very stable and resist air oxidation. Carbonyl clusters of group 9 elements containing even more than 20 metal atoms are now known [M6(CO)i5] - (M = Co, Rh, Ir), lM CO)uT. [M6(CO)i5C]"-(M = Co,Rh), [Co8(CO),sC] -, [Rh,(CO)i,] -, [Rh8(CO)i,C], [Ir8(CO)22]"-,... 

C = aliphatic primary, secondary or tertiary carbon atom, aryl or heteroaryl carbon atom carbonyl carbon atom CPE = chlorinated phosgene equivalent... 

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