This paper reports the synthesis and characterization of chlorobis(pentamethylcyclopentadienyl)thorium and -uranium dialkylamides, M[η-(CH3)5C5]2(NR2)Cl (M = Th, U; R = CH3, C2H5), and bis(dialkylamides), M[η-(CH3)5C5]2(NR 2)2 (M = Th, U, R = CH3; M = U, R = C2H5). NMR studies indicate restricted rotation about the M-NR2 bonds. The amide compounds undergo facile migratory insertion of carbon monoxide to produce the corresponding η2-carbamoyl complexes M[η-(CH3)5C5]2[η 2-CONR2]Cl, M[η-(CH3)5C5]2[η 2-CONR2]NR2, and M[η-(CH3)5C5]2[η 2-CONR2]2 which were characterized by a variety of chemical and physicochemical methods. The infrared spectra of these compounds exhibit unusually low C-O stretching frequencies (1490-1560 cm-1) for carbamoyl complexes, indicative of strong metal-oxygen bonding. The molecular structures of Th[η-(CH3)5C5]2[η 2-CON(C2H5)2]Cl and U[η-(CH3)5C5]2[η 2-CON(CH3)2]2 have been determined by single-crystal X-ray diffraction techniques. The former complex crystallizes in the monoclinic space group P21/n (an alternate setting of P21/c - C2h 5) with four molecules in a cell of dimensions: a = 9.097 (2) Å, b = 21.291 (4) Å, c = 14.031 (2) Å, and β = 95.78 (2)°; the latter complex crystallizes in the monoclinic space group P21/c - C2h 5/; with four molecules in a unit cell of dimensions: a = 9.277 (4) Å, b = 16.143 (5) Å, c = 18.977 (6) Å, and β = 130.55 (3)°. For the chloro complex, least-squares refinement led to a value for the conventional R index (on F) of 0.080 for 3156 independent reflections having 2θMoKᾱ <55° and I > 3σ(I), while for the bis(carbamoyl), least-squares refinement led to a conventional R (on F) of 0.036 for 3689 independent reflections having 2θMoKᾱ <55° and I > 3σ(I). The M[(CH3)5C5]2 fragments of both molecules are of the "bent sandwich" M(C5H5)2X2 configuration, with the carbamoyl ligands bound in a η2 fashion. The chloro complex is disordered, with two isomers (one with the C-O vector pointing toward the Cl atom, one with it pointing away) having cocrystallized in nearly equal proportions. The Th-O distances are 2.383 (31) and 2.460 (16) Å; the average Th-C distance is 2.418 (20) Å; the Th-C-O angles accompanying the above distances are 70.1 (15) and 74.5 (1)°, respectively. In solution, the two isomers of the analogous uranium complex are in equilibrium (ΔH = 1.2 ± 0.1 kcal/mol; ΔS = 8 ± 1 eu) with interconversion rapid on the 1H NMR time scale at room temperature (at -80°C, ΔG‡ = 8.9 ± 0.5 kcal/mol). In the bis(carbamoyl), the U-O distances are 2.370 (5) and 2.342 (7) Å, the corresponding U-C distances 2.405 (8) and 2.402 (9) Å;, and the corresponding U-C-O angles 73.0 (4) and 71.8 (5)°. The structural and spectral data evidence dative nitrogen lone-pair donation to the "carbenoid" carbamoyl carbon atom. The complex Th[η-(CH3)5C5]2[N(CH 3)2]CH3 was also prepared; carbonylation occurs preferentially at the metal-carbon bond to yield Th[η-CH3)5C5]2[N(CH 3)2](η2-COCH3).
|Number of pages||15|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 1981|
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