Thiapentadienyl-rhodium-phosphine chemistry

John R. Bleeke, Monica Shokeen, Eric S. Wise, Nigam P. Rath

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The reactions of (Cl)Rh(PR 3) 3 (R = Me, Et) with the anionic thiapentadienide reagent lithium 2,3-dimethyl-5-thiapentadienide have been investigated, Treatment of (Cl)Rh(PMe 3) 3 with lithium 2,3-dimethyl5-thiapentadienide produces ((1,2,5-η)-2,3-dimethyl-5- thiapentadienyl)Rh(PMe 3) 3 (1), in which the thiapentadienyl ligand is σ-bonded to rhodium through the sulfur end of the chain and π-bonded through the carbon end (C1-C2 double bond). In solution at room temperature, 1 undergoes a rapid dynamic process involving release and recoordination of the thiapentadienyl double bond C1-C2, causing two of the phosphine ligands to become equivalent. The intermediate in which the double bond C1-C2 is released from the rhodium center can be "trapped" as a dioxygen adduct, ((5-η)-2,3-dimethyl-5-thiapentadienyl)Rh(PMe 3) 32-O 2) (2). When it is stirred at room temperature in tetrahydrofuran solution, 1 slowly rearranges to ((1,4,5-η)-2,3-dimethyl-5-thiapentadienyl)Rh(PMe 3) 3 (3), the thermodynamic isomer in which the thiapentadienyl ligand is π-bonded through the carbon end of the chain (Cl) and σ-bonded through the sulfur end (C4-S double bond). The reactions of both the kinetic and thermodynamic products (1 and 3, respectively) with simple electrophiles have been investigated. Treatment of 1 and 3 with HBF 4· OEt 2 results in proton addition to the thiapentadienyl carbon C1 and production of the sulfur-bridged dimer {[((2,3,4,5-η)-2,3-dimethyl-5-thiapentadiene) Rh(PMe 3) 2] 2} 2+(BF 4 -) 2 (4). In contrast, treatment of 1 and 3 with CH 3O 3SCF 3 leads to methylation at the nucleophilic sulfur centers and production of [((1,2,3,4-η)-2,3,5-trimethyl- 5-thiapentadiene)Rh(PMe 3) 3] +O 3SCF 3 - (5) and [((1,4,5-η)-2,3,5-trimethyl- 5-thiapentadienyl)Rh(PMe3)3]+O 3SCF 3 - (6), respectively. When 3 is reacted with methylene chloride (CH 2Cl 2), a double displacement of chlorides by the nucleophilic sulfurs in two molecules of 3 leads to a novel methylene-bridged dimer (7). Treatment of (Cl)Rh(PEt 3) 3 with lithium 2,3-dimethyl-5-thiapentadienide produces ((5-η)-2,3-dimethyl-5-thiapentadienyl)Rh(PEt 3) 3 (8). Unlike 1, the terminal carbon-carbon double bond in 8 remains uncoordinated to rhodium due to steric constraints. A sulfur-bridged dimer, [((5-η)-2,3-dimethyl-5-thiapentadienyl)Rh(PEt 3) 2] 2 (9), results when 8 is dissolved in acetone at room temperature. The thiapentadienyl bonding mode in 9 is identical with that in 8, and 9 readily converts back to 8, upon treatment with PEt 3 in tetrahydrofuran. In toluene solution at room temperature, 8 isomerizes to a second sulfur-bridged dimer, [((1,4,5-η)-2,3-dimethyl-5-thiapentadienyl)Rh(PEt 3) 2] 2 (10), in which the thiapentadienyl ligand has rearranged to the same mode as observed in 3. Dimer 10 is produced as a 4:1 mixture of two isomers, a trans isomer (10a) possessing inversion symmetry and a cis isomer (10b) with C 2 symmetry. The trans isomer 10a reacts with small ligands, L, to produce mixed dimers of formula [((1,4,5-η)-2,3- dimethyl-5-thiapentadienyl)Rh(PEt 3)(L)] 2 (12a, L = PMe 3; 13a, L = CNCMe 3), in which the trans geometry is retained. Compounds 1-4, 7, 9, 10a, lib (the (PMe 3) 4 analogue of 10b), 12a, and 13a have been characterized by single-crystal X-ray diffraction.

Original languageEnglish
Pages (from-to)2486-2500
Number of pages15
Issue number10
StatePublished - May 8 2006

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    Bleeke, J. R., Shokeen, M., Wise, E. S., & Rath, N. P. (2006). Thiapentadienyl-rhodium-phosphine chemistry. Organometallics, 25(10), 2486-2500.