Synthesis of a Cyclic Co2Sn2 Cluster Using a Co- Synthon.

[Ar'SnCo]2 (1, Ar' = C6H3-2,6{C6H3-2,6- iPr2}2), a rare metal-metal bonded cobalt-tin cluster with low-coordinate tin atoms, was prepared by the reaction of [K(thf)0.2][Co(1,5-cod)2] (cod = 1,5-cyclooctadiene) with [Ar'Sn(µ-Cl)]2. This reaction illustrates a promising synthetic strategy to access uncommon metal clusters. The structure of 1 features a rhomboidal Co2Sn2 core with strong metal-metal bonds between tin and cobalt and a weaker tin-tin interaction. Reaction of 1 with white phosphorus afforded [Ar'2Sn2Co2P4] (2), the first molecular cluster compound containing phosphorus, cobalt and tin.

Dynamic Behavior and Isomerization Equilibria of Distannenes Synthesized by Tin Hydride/Olefin Insertions: Characterization of the Elusive Monohydrido Bridged Isomer.

The tin(II) hydride [AriPr6Sn(µ-H)]2(AriPr6 = C6H3-2,6(C6H2-2,4,6-iPr3)2) (1a) reacts with 2 equiv of ethylene or t-butylethylene at ca. 25 °C to yield Sn2(AriPr6)2R2(R = ethyl or t-butylethyl), which exist either as a symmetric distannene AriPr6(R)SnSn(R)AriPr6 (2a or 5a) or an unsymmetric stannylstannylene AriPr6SnSnR2AriPr6 (3a). In contrast, the less crowded Sn(II) hydride [AriPr4Sn(µ-H)]2 (AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2) (1b) reacts with excess ethylene to give AriPr4(CH2CH3)2Sn(CH2CH2)Sn(CH2CH3)(CHCH2)AriPr4 (4) featuring five ethylene equivalents, one of which is dehydrogenated to an vinyl, -CH═CH2, group. The AriPr4 isomers of 2a and 3a, i.e., [AriPr4Sn(C2H5)]2 (2b) and AriPr4SnSn(C2H5)2AriPr4 (3b) are obtained by reaction of [AriPr4Sn(µ-Cl)]2 with EtLi or EtMgBr. The isomeric pairs 2a and 3a are separated by crystallization at different temperatures. Variable-temperature 1H NMR spectroscopy indicates fast ethyl group exchange between Ar(C2H5)SnSn(C2H5)Ar (Ar = AriPr6 (2a) or AriPr4 (2b)) and ArSnSn(C2H5)2Ar (Ar = AriPr6 (3a) or AriPr4 (3b)) with ΔG⧧ = 14.2 ± 0.65 kcal mol-1 for 2a/3a and 14.8 ± 0.36 kcal mol-1 for 2b/3b. The bulkier distannenes [ArSn(CH2CH2tBu)]2 (Ar = AriPr6 (5a) or AriPr4 (5b)), obtained from 1a or 1b and t-butylethylene, dissociate to ArSnCH2CH2tBu monomers in solution. At lower temperature, they interconvert with their stannylstannylene isomers with parameters Keq = 4.09 ± 0.16 for 5a and 6.38 ± 0.41 for 5b and ΔGeq = -1.81 ± 0.19 kcal mol-1 for 5a and -1.0 ± 0.03 kcal mol-1 for 5b at 298 K. The 1:1 reaction of 1a or 1b with 5a or 5b yields the unknown monohydrido species Sn2RHAr2 which has the structure AriPr6Sn-Sn(H)(CH2CH2tBu)AriPr6 (6a) or the monohydrido bridged AriPr4S n(µ-H)S n(CH2CH2tBu)AriPr4 (6b). The latter represents the first structural characterization of a monohydrido bridged isomer of a ditetrelene.

Tin(II) Hydrides as Intermediates in Rearrangements of Tin(II) Alkyl Derivatives.

Reactions of the Sn(II) hydrides [ArSn(µ-H)]2 (1) (Ar = AriPr4 (1a), AriPr6 (1b); AriP4 = C6H3-2,6-(C6H3-2,6-iPr2)2, AriPr6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2) with norbornene (NB) or norbornadiene (NBD) readily generate the bicyclic alkyl-/alkenyl-substituted stannylenes, ArSn(norbornyl) (2a or 2b) and ArSn(norbornenyl) (3a or 3b), respectively. Heating a toluene solution of 3a or 3b at reflux afforded the rearranged species ArSn(3-tricyclo[2.2.1.02,6]heptane) (4a or 4b), in which the norbornenyl ligand is transformed into a nortricyclyl group. 1H NMR studies of the reactions of 4a or 4b with tert-butylethylene indicated the existence of an apparently unique reversible ß-hydride elimination from the bicyclic substituted aryl/alkyl stannylenes 2a or 2b and 3a or 3b. Mechanistic studies indicated that the transformation of 3a or 3b into 4a or 4b occurs via a ß-hydride elimination of 1a or 1b to regenerate NBD. Kinetic studies showed that the conversion of 3a or 3b to 4a or 4b is first order. The rate constant k for the conversion of 3a into 3b was determined to be 3.33 × 10-5 min-1, with an activation energy Ea of 16.4 ± 0.7 kcal mol-1.