The heteroleptic organotin(II) halides {2,6-[P(O)(OEt) 2 ] 2 -4-tert-Bu-C 6 H 2 }SnX (1, X ) Cl; 2, X ) Br) have been prepared starting from {2,6-[P(O)(OEt) 2 ] 2 -4-tert-Bu-C 6 H 2 }Li and SnX 2 and have been used as precursors for the preparation of the heteroleptic stannylenes {2,6-Multinuclear ( 1 H, 13 C, 31 P, 119 Sn) NMR of all compounds, 119 Sn Mo ¨ssbauer spectra of 1 and 10, and single-crystal X-ray structure analyses of 6, 8, and 12 are reported. The derivatives 6, 7, and 7a are rare examples of compounds containing Sn-(II)-Si(IV) and Sn(II)-Sn(IV) bonds, respectively.

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The intramolecularly coordinated triorganotin hexafluorophosphate {4-t-Bu-2,6-[P(O)(Oi-Pr)2]2C6H2}SnPh2 +PF6 - (3a) was prepared by reaction of the [4+2]-coordinated tetraorganotin compound {4-t-Bu-2,6-[P(O)(Oi-Pr)2]2C6H2}SnPh3 (2a) with Ph3C+PF6 - and shown to react under intramolecular cyclization with bromide and fluoride ion, respectively, as well as with water to give the intramolecularly coordinated benzoxaphosphastannole [1(P),3(Sn)-SnPh2OP(O)(Oi-Pr)-6-t-Bu-4-P(O)(Oi-Pr)2]C6H2 (4a). Analoguously, the in situ-generated intramolecularly coordinated triorganosiliconium hexafluorophosphate {4-t-Bu-2,6-[P(O)(OEt)2]2C6H2}SiPh2 +PF6 - (6) reacts with water to give the corresponding intramolecularly coordinated benzoxaphosphasilole [1(P),3(Si)-P(O)(OEt)OSiPh2-6-t-Bu-4-P(O)(OEt)2]C6H2 (7). Isotope-labeling experiments with H2 18O in combination with electrospray mass spectrometric studies reveal that in the case of the organotin compound 3a the cyclization exclusively proceeds via nucleophilic attack of water at the POC-carbon. In contrast, two pathways account for the formation of the benzoxaphosphasilole 7, that is, attack of water at the POC-carbon as well as at phosphorus. The latter pathway either is in contrast to the axial entry−axial departure principle of nucleophilic substitution at phosphorus or indicates Berry pseudorotation involving a five-membered chelate ring. The molecular structure of 3a was determined by single-crystal X-ray diffraction analysis.

New intramolecularly coordinated organotin compounds containing the monoanionic O,C,O‐coordinating ligand {4‐tert‐Bu‐2,6‐[P(O)(OEt)2]2C6H2}− have been synthesized by substitution reactions starting from organotin halides. In view of the enhanced reactivity of the intramolecularly coordinated compounds {4‐tert‐Bu‐2,6‐[P(O)(OEt)2]2C6H2}SnR2R′ (2, R = Ph, R′ = CH2SiMe3; 3, R = R′ = Ph; 6, R = R′ = Cl), cationic tin species are suggested to occur as intermediates in the formation of the heterocyclic compounds [1(Sn),3(P)‐Ph2SnOP(O)(OEt)‐5‐tert‐Bu‐7‐P(O)(OEt)2]C6H2 (8), [1(Sn), 3(P)‐Ph(Me3SiCH2)SnOP(O)(OEt)‐5‐tert‐Bu‐7‐P(O)(OEt)2]C6H2 (15), and {[1(Sn),3(P)‐Cl2SnOP(O)(OEt)‐5‐tert‐Bu‐7‐P(O)(OEt)]C6H2}2 (16). The latter compounds are formed by intramolecular cyclizations of pentacoordinate cationic tin species under elimination of ethyl halide. Furthermore, the synthesis of [1(Sn),3(P)‐Ph2SnOP(O)(OH)‐5‐tert‐Bu‐7‐P(O)(OH)2]C6H2 (13) is described. Reaction of 8 with an excess of Me3SiBr leads to the unexpected formation of {2‐[P(O)(OEt)(OSiMe3)]‐4‐tert‐Bu‐6‐[P(O)(OEt)2]C6H2}SnPhBr2 (9) as a result 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]2C6H2}− are demonstrated by X‐ray diffraction analyses of the tetraorganotin compound 2 and the monoorganotin trichloride 6. Furthermore, the molecular structures of the 2,3,1‐oxaphosphastannoles 8 and 16 are discussed.

The syntheses of the intramolecularly coordinated organotin-substituted transition metal complexes [RSn{W(COand [RSn{W(CO) 3 Cp}-Cr(CO) 5 ] (5, R = 4-t-Bu-2,6-{P(O)(OEt) 2 } 2 C 6 H 2 ) are reported. The reaction of compound 2 with Ph 4 P + Br¯gave the benzoxaphosphastannole [1(P),3(Sn)-Sn[W(CO) 3 Cp] 2 OP(O)(Oi-Pr)-6-t-Bu-4-P(O)(Oi-Pr) 2 -C 6 H 2 ] (3). The compounds are characterized by 1 H, 13 C, 31 P, 119 Sn NMR and IR spectroscopy and, except for 3, by single crystal X-ray diffraction analysis. The experimental work is accompanied by DFT calculations.