SYNTHESIS, STRUCTURE, AND REACTIVITY OF CYCLIC (ARENE)CHROMIUM CARBENE COMPLEXES

In contrast to benzannulation products obtained by photolysis, thermolysis of the chromium carbene complexes [(1,1'-biphenyl-2-yl)methoxymethylene]pentacarbonylchromium (1) and [(1,1'-biphenyl-2-yl)(dimethylamino)methylene]pentacarbonylchromium (4) provide the new cyclic arene carbene complexes {[(1',2',3',4',5',6'-eta)-1,1'-biphenyl-2-yl]methoxymethylene}dicarbonylchromium (3) and {[(1',2',3',4',5',6'-eta)-1,1'-biphenyl-2-yl](dimethylamino)methylene}dicarbonylchromium (5). The C-13 NMR spectra of these new complexes have unusually high-field-shifted and low-field-shifted signals for the carbene and carbonyl carbon resonances, respectively. The complexes are remarkably stable and do not show the high electrophilic behavior typical of Fischer carbene complexes. A new protocol for the aminolysis of Fischer carbene complexes is reported. The structure of complexes 3 and 5 were determined by single-crystal X-ray diffraction studies. 3 crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 16.154 (2) angstrom, b = 12.256 (2) angstrom, c = 15.575 (2) angstrom, and beta = 122.92 (1)-degrees, with Z = 8. 5 crystallizes in the monoclinic space group P2(1)/n with unit cell dimensions a = 11.47 (1) angstrom, b = 7.082 (7) angstrom, c = 20.87 (2) angstrom, and beta = 108.13 (2)-degrees, with Z = 4. The structures were refined by full-matrix least-squares procedures to final R = 0.028 and R(w) = 0.050 for 2074 unique observed reflections for 3 and R = 0.066 and R(w) = 0.101 for 1580 unique observed reflections for 5.