CYCLOMETALATION OF ORTHO-ARYLPHENOXIDE AND ALKOXIDE LIGANDS AT TIN(IV) METAL CENTERS - REACTION SCOPE AND PRODUCT CHARACTERIZATION

The reaction of LiOC6H3Ph2-2,6 (OC6H3Ph2-2,6 = 2,6-diphenylphenoxide) with SnCl4 leads to the formation of the dimeric compound [Sn(OC6H3Ph-C6H4)Cl2]2 (1) containing cyclometalated 2,6-diphenylphenoxide ligands. Similarly, treatment of Sn(NMe2)4 with HOC6H3Ph2-2,6 (2 equiv) in hydrocarbon solvents at 50-degrees-C leads to the bis-cyclometalated compound [Sn(OC6H3Ph-C6H4)2(HNMe2)2] (2). Single-crystal X-ray diffraction analyses of 1 and 2 show the presence of six-membered metallacycle rings formed by metalation of a substituent aryl group of the aryloxide ligands. In compound 1 the dinuclear unit is held together by asymmetric oxygen bridges, while in 2 the dimethylamine ligands are mutually cis. Attempts to induce cyclometalation of 2,6-diphenylphenoxide ligands utilizing an alkyl leaving group at tin failed. Compounds [Me3Sn(OC6H3Ph2-2,6)] (3) and [Me2Sn(OC6H3Ph2-2,6)2] (4) are stable at 150-degrees-C for days. The treatment of Sn(NMe2)4 with the asymmetric phenol HOC6H2Bu(t)2-2,4-Ph-6 initially led to the bis-substituted compound [Sn(OC6H2Bu(t)2-2,4-Ph-6)2(NMe2)2] (5). Thermolysis of 5 leads to the five-coordinate, bis-cyclometalated compound [Sn(OC6H2Bu(t)2-C6H4)2(HNMe2)] (6). No evidence for metalation of the tert-butyl substituent was observed. The solid-state structure of 6 shows the geometry about tin to be trigonal bipyramidal with trans, axial oxygen atoms. Treatment of Sn(NMe2)4 with various alcohols containing aryl substituents leads to the isolation of the alkoxide compounds [Sn(OCH2Ph)4(HNMe2)]2 (7), [Sn(OCMe2Ph)4] (8), and [Sn(OCPh3)2(NMe2)2] (9). A single-crystal X-ray diffraction analysis of 7 shows a dinuclear unit held together by two alkoxide bridges. The dimethylamine ligands occupy axial sites in the edge-shared bis-octahedral structure, which contains a crystallographic inversion center. Thermolysis at 110-degrees-C of the 2-phenylpropoxide compound 8 results in elimination of HOCMe2Ph and formation of a bis-cyclometalated complex [Sn(OCMe2-C6H4)2]2 (10). Crystallographic studies show the dinuclear unit in 10 is held together by two bridging oxygen atoms within two of the new five-membered metallacycle rings. The spectroscopic properties of 7 and 10 are consistent with the dinuclear units being maintained in solution. Thermolysis of the bis(amido) complex [Sn(OCPh3)2(NMe2)2] (9) also leads to a bis-cyclometalated compound [Sn(OCPh2-C6H4)2(HNMe2)2] (11). The solid-state structure of octahedral 11 shows the dimethylamine ligands to be mutually trans. In a related study, treatment of Sn(NMe2)4 with 2-tert-butyl-1-naphthol (HO-tbn) initially leads to the intermediate [Sn(O-tbn)2(NMe2)2], which converts slowly at room temperature to the bis-cyclometalated complex [Sn(O-tbn-H)2(NHMe2)2] (12). The cyclometalation of the O-tbn ligands at the 8-position of the naphthalene ring was confirmed by a single-crystal X-ray diffraction analysis of 12. Crystal data: for Sn2Cl4O2C42H30 (1) at 20-degrees-C, a = 11.680 (1) angstrom, b = 26.909 (3) angstrom, c = 12.884 (1) angstrom, beta = 110.720 (8)-degrees, Z = 4, d(calc) = 1.659 g cm-3 in space group P2(1)/n; for SnO2N2C40H38 (2) at 22-degrees-C, a = 18.223 (1) angstrom, b = 7.644 (2) A, c = 13.709 (1) angstrom, beta = 121.440 (7)-degrees, Z = 2, d(calcd) = 1.422 g cm-3 in space group C2; for SnO2NC42H55 (6) at 20-degrees-C, a = 20.878 (3) angstrom, b = 7.024 (1) angstrom, c = 27.150 (3) angstrom, beta = 95. 37 (1)-degrees, Z = 4, d(calcd) = 1.214 g cm-3 in space group P2(1)/n; for Sn2O8N2C60H70 (7), a = 10.701 (2) angstrom, b = 11.208 (1) angstrom, c = 23.322 (2) angstrom, alpha = 91.386 (9)-degrees, beta = 98.05 (1)-degrees, gamma = 92.62 (1)-degrees, Z = 2, d(calcd) = 1.423 g cm-3 in space group P1BAR; for Sn2O4C36H40 (10) at 20-degrees-C, a = 24.101 (2) angstrom, b = 9.972 (1) angstrom, c = 19.678 (1) angstrom, beta = 135.489 (8)-degrees, Z = 4, d(calcd) = 1.551 g cm-3 in space group C2/c; for SnO2N2C42H42 (11) at 20-degrees-C, a = 9.175 (1) angstrom, b = 9.3158 (9) angstrom, c = 12.033 (2) angstrom, alpha = 76.20 (1)-degrees, beta = 68.03 (1)-degrees, gamma = 67.65 (1)-degrees, Z = 1, d(calcd) = 1.374 g cm-3 in space group P1BAR; for SnO2N2C32H42 (12) at 20-degrees-C, a = 10.3832 (9) angstrom, b = 9.075 (1) angstrom, c = 17.255 (2) angstrom, beta = 112.600 (8)-degrees, Z = 2, d(calcd) = 1.339 g cm-3 in space group P2(1)/c.