Intramolecular donor-assisted cyclization of organotin compounds

New intramolecularly coordinated organotin compounds containing the monoani onic O,C,O-coordinating ligand (4-tert-Bu-2,6-[P(O)(OEt)(2)](2)C6H2)(-) hav e been synthesized by substitution reactions starting from organotin halide s. In view of the enhanced reactivity of the intramolecularly coordinated c ompounds [4-tert-Bu-2,6-(P(O)(OEt)(2)](2)C6H2)SnR2R' (2, R = Ph, R' = CH2Si Me3i; 3, R = R' = Ph; 6, R = R' = Cl), cationic tin species are suggested t o occur as intermediates in the formation of the heterocyclic compounds [1( Sn),3(P) ph(2)snOP(o)(oEt)-5-tert-Bu-7-P(O) (OEt)(2)]C6H2 (8), [1(Sn), 3(P) -Ph(Me(3)siCH(2))snOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)(2)]-C6H2 (15), and {[1 (Sn),3(P)-Cl2SnOP(O)(OEt)-5-teri-Bu-7-P(O)(OEt)]C6H2}(2) (16). The latter c ompounds are formed by intramolecular cyclizations of pentacoordinate catio nic tin species under elimination of ethyl halide. Furthermore, the synthes is of [1(Sn),3(P)-Ph2SnOP(O)(OH)-5-tert-Bu-7-P(O)-(OH)(2)]C6H2 (13) is desc ribed, Reaction of 8 with an excess of Me3SiBr leads to the unexpected form ation of {2[P(O)(OEt) (OSiMe3)]-4-tert-Bu-6-[P(O)(OEt)(2)]C6H2}S(9) as a re sult of an O-Sn bond cleavage initiated by Me3SiBr and subsequent reaction of the intermediate with further Me3SiBr under Sn-C bond cleavage, The high donor capacity and the rigidity of the new ligand {4-tert-Bu-2,6-[P(O)(OEt )(2)](2)C6H2}(-) are demonstrated by X-ray diffraction analyses of the tetr aorganotin compound 2 and the monoorganotin trichloride 6. Furthermore, the molecular structures of the 2,3,1-oxaphosphastannoles 8 and 16 are discuss ed.