Synthesis and characterization of the cycloheptatrienyl tantalum "mixed-sandwich" compounds (c5r5)ta(c7h7).
Inorg Chem
; 47(2): 535-42, 2008 Jan 21.
Article
in En
| MEDLINE
| ID: mdl-18161962
ABSTRACT
The molecule (cycloheptatrienyl)(cyclopentadienyl)tantalum, (C(5)H(5))Ta(C(7)H(7)) (1), and its methylcyclopentadienyl and pentamethylcyclopentadienyl analogues (C(5)H(4)Me)Ta(C(7)H(7)) (2), and (C(5)Me(5))Ta(C(7)H(7)) (3) have been synthesized by magnesium reduction of the corresponding (C(5)R(5))TaCl(4) species in the presence of cycloheptatriene. The crystal structures of 2 and 3 show that the two rings are planar and essentially parallel to each other. Interestingly, the Ta-C distances to the C(7)H(7) ring are significantly shorter (by about 0.1 A) than those to the cyclopentadienyl ring; the difference reflects stronger bonding to the C(7)H(7) ring. A comparison with the structures of other (C(5)R(5))M(C(7)H(7)) shows that the M-C distances to the seven-membered ring are especially sensitive to the d-orbital energies of the metal center and its ability to engage in delta bonding with the ring. For 1-3, the EPR spectra at room temperature consist of octets due to the tantalum nuclear spin. Both A(iso) and g(iso) increase as the number of methyl groups on the cyclopentadienyl ring increases. EPR spectra of 1-3 as frozen glasses correspond to axial symmetry, and the hyperfine couplings and g factors are deduced from simulations.
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Collection:
01-internacional
Database:
MEDLINE
Language:
En
Journal:
Inorg Chem
Year:
2008
Document type:
Article
Affiliation country:
Estados Unidos