Structural diversity in organotin compounds derived from bulky monoaryl phosphates: dimeric, tetrameric, and polymeric tin phosphate complexes

Abstract

Monoaryl phosphates with a bulky aryl substituent have been used to synthesize new organotin clusters and polymers. The equimolar reaction between 2,6-diisopropylphenylphosphate (dipp-H₂) and Me₂SnCl₂ in ethanol at 25 °C leads to the formation of [Me₂Sn(μ₃-dipp)]_n (1), while the reaction of 2,6-dimethylphenylphosphate (dmpp-H₂) with Me₂SnCl₂ in either a 1:1 or 2:1 molar ratio proceeds to produce exclusively [Me₂Sn(μ-dmpp-H)₂]_n.nH₂O (2). Compounds 1 and 2 are 1D polymers with different architectures. In compound 1, the tin atom is five-coordinate (trigonal bipyramidal). Each dipp ligand bridges three different tin atoms to form an infinite ladder-chain structure. In 2, each six-coordinate (octahedral) tin atom is surrounded by four phosphate oxygen atoms originating from four different bridging dmpp-H ligands, thus forming a spirocyclic coordination polymeric chain. The use of nBu₂SnO as the diorganotin source in its reaction with dipp-H₂ leads to the isolation of dimeric [nBu₂Sn(μ-dipp-H)(dipp-H)]₂ (4), which contains a central Sn₂O₄P₂ unit. There are two chemically different half molecules of 4 in the asymmetric part of the unit cell and hence it actually exists as a 1:1 mixture of [nBu₂Sn(μ-dipp-H)(dipp-H)]₂ and [nBu₂Sn(μ-dipp)(dipp-H₂)]₂ in the solid state. The reaction of the monoorgano tin precursor nBuSn(O)(OH)·xH₂O with dipp-H₂ takes place in acetone at room temperature to yield the tetrameric cluster 5, which has different structures in the solution and in the solid state. ³¹P NMR spectroscopy clearly suggests that 5 has the formula [nBu₄Sn₄(μ-O)₂((μ-dipp-H)₈] in solution. The single-crystal X-ray diffraction studies in the solid state, however, reveal that compound 5 exists as [nBu₄Sn₄(μ-OH)₂(μ-dipp-H)₆(μ-dipp)₂]. The use of compounds 1-4 as possible precursors for the preparation of ceramic tin phosphate materials has been investigated. The thermolysis of 1 at 500 °C leads to the formation of quantitative amounts of Sn₂P₂O₇, while the thermolysis of 2, 3, and 4 under similar conditions results in the formation of SnP₂O₇.