UNUSUAL IRON(IV) COMPLEXES - METAL ATOM SYNTHESES AND STUDIES OF (ETA(6)-ARENE)FE(H)(2)(SICL3)(2) (ARENE EQUALS BENZENE, TOLUENE, P-XYLENE)

Iron atoms codeposited with excess arene (benzene, toluene, or p-xylene) at -196 or -78 degrees C yielded a brown matrix containing arene-solvated iron atoms. Treatment of this matrix with a limited amount of HSiCl3 produced novel Fe(IV) arene compounds. We have obtained and structurally characterized the following substances: 1, (eta(6)-benzene)Fe(H)(2)(SiCl3)(2), space group Pnma, a 15.244(2) Angstrom, b = 11.115(1) Angstrom, c = 8.309(1) Angstrom, Z = 4, V = 1407.9(5) Angstrom(3); 2, (eta(6)-toluene)Fe(H)(2)(SiCl3)(2), space group P2(1)/a, a = 12.232(2) Angstrom, b = 8.591(1) Angstrom, c = 13.873(2) Angstrom, beta = 92.66 (2)degrees, Z = 4, V = 1456.3 (6) Angstrom(3); 3, (eta(6)-p-xylene)Fe(H)(2)(SiCl3)(2), space group P2(1)/a, a = 8.323(1) Angstrom, b = 24.302(2) Angstrom, c = 8.627(1) Angstrom, beta = 116.541(9)degrees, Z = 4, V = 1561.2(7) Angstrom(3). In the NMR, the Si-29-H-1 coupling constants have been observed to be 15 Hz for all three compounds, dramatically lower than (1)J(Si-H) = 370 Hz for HSiCl3. The structural and NMR data show that the oxidative addition of H-SiCl3 to the Fe center is complete and these compounds are formally Fe(IV) dihydride derivatives. The interaction between arene and Fe is very strong; no arene exchange has been observed, even at elevated temperatures. Thermal decomposition appears to proceed by HSiCl3 reductive elimination. In addition, the first reaction of added ligands causes HSiCl3 elimination.