U-C a bond

They were independently synthesized by three independent research groups at the start of the 1970s and represent the first compounds to have well-defined actinide-carbon a bonds (structures for M = U R, e.g., Bu, CH2C6H4CH3, etc). (See, e.g., the papers by T.J. Marks group in 7. Am. Chem. Soc., 1973, 95, 5529 1976, 98, 703.) Thermally stable in vacuo, they react with methanol, forming MCp3(OMe) and RH. A low-temperature NMR smdy of [UCpsPr ] indicates restricted rotation about the U-C a bond at low temperatures. 

One of the decomposition products if I and II is ferrocene. This ds viewed as further evidence that these Cp U-R complexes decompose by the intramolecular proton abstraction mechanism as seen in the "monomer organoactinide (27, 36). The mass spectrum of I reveals that a cyclopentadienyl ring is lost first (presumably from Cp U) in preference to cleavage of the U-C a bond. 

Figure 2. A view of one of the two crystallographlcally Independent molecules of U(C5H5)3teCH in a unit cell. The U-C(a) bond distance is 2.36(3)A. From reference 17.

The unsymmetrical diene ligands in 85b and 85c may form two dia-stereomers with the less substituted double bond in the cis or trans configuration with respect to the Mo—C a bond. For 85b, only the isomer with the less substituted double bond cis to this bond is found. Compound 85c forms both isomers, but the cis isomer is distinctly preferred. In contrast with the fluxional >j2-diene complexes 84a-84c, compounds 85a-85c do not show temperature-dependent H-NMR spectra for the //4-diene ligands. However, this does not disprove a hindered rotation of the f/4-diene ligands when one of the two conformers (o or u) is energetically more favored than the other. 

The crystal structure of the C2H5NC adduct shows a quasitetrahe-dral arrangement of the ligands around the uranium. The U-C-N bond angle is large (173°) but not linear (389). 

The U-C o bond distance of 2 33 (2) 8 is at least 0.3 A shorter. than the mean uranium-(q -C H ) distance (2.688). The shortening can be attributed to the o-bonded nature of the phenylacetylide group, supporting evidence for which was reported by Atwood when he determined the U-Co bond distance in (C H )-U-C=CH to be 2.368 (30). Unfortunately, crystallographic difri-culties limited the accuracy of the observed U-C o bond distance... 

Evidence for a U-C double bond has been presented for the compound ( 7=-Cp)3UCHPMe2Ph ... 

The co-ordination geometry of [U(7i-C5H4 CH2Ph)3Cl], obtained by reaction of UCl, with TlCjH CHjPh, can be described as a distorted tetrahedron the U atom lies 0.43 A above a plane defined by the centres of the three n-bonded cyclopentadienyl rings (a displacement of 0.82 A was actually expected). In the quasi-tetrahedral [U(7t-CsH5)3C rPh], the U—C(acetylide) bond... 

Analysis of the ELF has also been used to understand the bonding in the uranium methylidyne complexes XjUCH (X=F, Cl, Br) [9]. The ELF of each of these complexes was characterized by a ring-shaped disynaptic basin lying perpendicular to the U-C bond, a defining feature of the ELF in the prototypical C-C triple bond of ethyne, leading the authors to assert the existence of an unprecedented U-C triple bond. 

U(Tp )2CH2Ph] and the high thermodynamic stabihty of the +4 oxidation state.The trivalent uranium complex [U(Tp )2(CH2Ph)] has been investigated by DFT as catalyst to promote the fimctionahzation ofC02 and CS2-It has been found that the interaction between CO2 and CS2 is not with central uranium atom, but due to the steric hindrance the first step is the cleavage of the U—C benzyl bond to form a C—C covalent bond. " ... 

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