Six-coordinate carbon

Table I) are virtually planar with no atom displaced by more than 0.08 A from the least-squares plane defined by those six atoms. The dihedral angle between the plane formed by the six coordinated carbon atoms (Plane II) and that formed by the uncoordinated olefin (Plane III) are also identical (117°), within experimental error, in all three complexes (Table I). The longest C—F bond distances in 56a and 56b are those on the terminal ends of the coordinated triene, reflecting the considerable rehybridization toward pyramidal geometry at these carbon atoms. Surprisingly, the overall skeletal structure of 57b is not significantly different from those of the fluorinated analogues 56, and the observed differences in air and thermal stability are not manifested in significantly different Mn—C bond distances or in a different mode of metal-ligand bonding in 57b.

The dication (CgMefi)21 (437) and the CLi62+ dication (438) are two additional six-coordinate carbon-containing species. Ion 437 was observed by Hogeveen and... 

Other six-coordinate carbon-containing carbocations reported so far are the (23) and the CLie dication (24). Ion 23 was observed by... 

A general discussion has been given of the bond lengths involving six-coordinate carbon in carbaboranes C2B10H12, and their derivatives. ... 

The high coordination number of the carbon atom in these compounds has aroused some interest, but six-coordinate carbon is well known in metal carbides such as FcsC, in which the carbon atoms lie in the interstices of almost regular trigonal pyramidal prisms of iron atoms (382). 

Aurophilic interactions also play an important role in stabilizing the remarkable hypervalent compounds [(Ph3PAu)gC] + with a six-coordinate carbon atom [30], [(Ph3PAu)5C]+ with a five-coordinate carbon atom [31], and [(Ph3PAu)5N] + with a five-coordinate nitrogen atom [32] as seen in Figure 3.7. 

It is remarkable that chemists long resisted making the connection between boron and electron-deficient carbon, which, after all, are analogs. I was thus given the opportunity to be able to establish the general concept of five and six coordination of electron-deficient carbon and to open up the field of what I called hypercarbon chemistry. 

Six-coordination is obtained in [PtMe3(acac)]2 by bidentate (0,0 ) behaviour and by a bond to the 7-carbon, a situation maintained in solution at room temperature (on warming, the bond to the 7-carbon breaks). In the bipyridyl adduct, it is the bond to the 7-carbon that completes the octahedral coordination [192],... 

Reactions of the hydrido(hydroxo) complex 2 with several substrates were examined (Scheme 6-14) [6]. The reactions are fairly complicated and several different types of reachons are observed depending on the substrate. Methyl acrylate and small Lewis bases such as CO, P(OMe)3, BuNC coordinate to the five-coordinated complex 2 affording the corresponding six-coordinate complexes. In reactions with the unsaturated bonds in dimethylacetylenedicarboxylate, carbon dioxide, phenylisocyanate indications for the addition across the O-H bond but not across the Os-OH bond were obtained. In reactions with olefins such as methyl vinyl ketone or allyl alcohol, elimination of a water molecule was observed to afford a hydrido metalla-cyclic compound or a hydrido (ethyl) complex. No OH insertion product was obtained. 

Cyanide binds to a series of Ni complexes with N302 chelate ligands, and EPR spectra of the adducts indicate quasi-axial symmetry with a g pattern typical of low-spin, six-coordinate complexes with axial elongation and with a 2Ay ground state. No direct spin interaction of the unpaired electron with the carbon atom of the cyanide takes place.70... 

A cyclam derivative with an amine pendent donor attached at the bridgehead carbon atom was presynthesized from diethylaminomalonate and l,9-diamino-3,7-diazanonane in refluxing MeOH, followed by BH3-THF reduction.1507 It acts as a pentadentate ligand at pH 8.5 and forms a six-coordinate complex (592) with a water molecule sitting at the remaining axial site. 

Paoletti et al. used a mixed aza oxo macrocycle (53) to form (yu3-C03) carbonate species on absorption of atmospheric C02. The crystal structure showed a trimer with threefold symmetry and six-coordinate zinc centers.461 This was described as C02 fixation however, three equivalents of zinc complex are required for each C02 molecule and so it is not a catalytic process. 

In a manner similar to OsH(OH)(CO)(P Pr3)2, the hydride-metallothiol complex OsH(SH)(CO)(P Pr3)2 adds Lewis bases that are not bulky such as CO and P(OMe)3 to give the corresponding six-coordinate hydride-metallothiol derivatives OsH(SH)(CO)L(P Pr3)2 (L = CO, P(OMe)3). OsH(OH)(CO)(PiPr3)2 and OsH(SH)(CO)(P Pr3 also show a similar behavior toward dimethyl acetylenedi-carboxylate. Treatment of OsH(SH)(CO)(P Pr3)2 with this alkyne affords 6sH SC(C02Me)CHC(OMe)6 (CO)P Pr3)2, which is the result of the tram addition of the S—H bond to the carbon-carbon triple bond of the alkyne. Phenyl-acetylene, in contrast to dimethyl acetylenedicarboxylate, reacts with OsH(SH) (CO)(P Pr3)2 by insertion of the carbon-carbon triple bond into the Os—H bond to give the unsaturated alkenyl-metallothiol derivative Os ( )-CH=CHPh (SH) (CO)(P Pr3 )2, the inorganic counterpart of the organic a, (3-unsaturated mercaptans (Scheme 46).92... 

It is interesting to note that the decrease in metal electron density that accompanies the change from five- to six-coordinate geometry does not have a detectable effect on the metal-carbene carbon bond length in these complexes. The metal-carbyne carbon bond in several osmium carbyne... 

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