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Chemistry of o-Xylenediyl-Metal Complexes. Part 5. Silicon and Tin Metallacycles derived from o-C6H4(CHR)2 (R = H or SiMe3)

DOI: 10.1039/DT9920000775

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 775 - 786 (1992)

Update date:2022-07-30

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Authors:

Lappert, Michael F.Lappert, Michael F.

Leung, Wing-PorLeung, Wing-Por

Raston, Colin L.Raston, Colin L.

Skelton, Brian W.Skelton, Brian W.

White, Allan H.White, Allan H.

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Article abstract of DOI:10.1039/DT9920000775

Treatment of SnCl2Ph2 with 6 or 2 7 in OEt2 yields the stannacycle 1 or 2 ((LL)2- = o-C6H4(CH2)2, (L'L')2- = o-C6H42, thf = tetrahydrofuran, tmen = Me2N2NMe2).Likewise, SnCl4 with 6 or 7 at 30 deg C in OEt2 affords exclusively the stannaspirobicycle 3 or 4; by contrast SnCl4 with 7 at -78 deg C gives, together with 4 (52percent), the yellow, diamagnetic tin(II) metallacycle 5 (14percent).Compound 5 is more conveniently prepared by treating Sn(OC6H2But2-2,6-Me-4)2 with 7; it is tetrameric in the solid and in solution, but monomeric in the gas phase and has a low first ionisation energy (7.6 eV).The compound 8 is obtained by an in situ Grignard reaction from SiCl2Me2, o-C6H4(CH2Cl)2 and Mg in thf, while 9 is prepared from SiCl2Me2 and 7.Each of the metallacycles derived from the ligand (L'L')2- was obtained stereospecifically as the meso diastereomer.X-Ray structure determinations of complexes 1-5 have been performed.The α,α'-unsubstituted metallacycles have shorter α> distances (2.144 in 1, 2.147 Angstroem in 3) than the corresponding α,α'-bis(trimethylsilyl) derivatives (2.166 in 2, 2.174 Angstroem in 4).The C6CαCα-o-xylenediyl plane is folded relative to the MCαCα plane, the fold angle Θ being 8.5 (1), 19.8 (2), 0.8 and 11.9 (3) 24.1 and 23.0 (4) and 20.8 deg (5).The larger Θ values for the complexes 2 and 4 than for their counterparts 1 and 3 (as for comparable SnC-α distances) is attributable to greater interligand strain and crowding around the metal centre in 2 and 4.Molecules of 5 have 4 symmetry, with Sn-Sn 2.852(3), Sn-Cα 2.15(3) and Sn-Cα' 2.09(4) Angstroem.

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