Carbon-Carbon vs Carbon-Hydrogen Bond Activation by Ruthenium(II) and Platinum(II) in Solution

TY - JOUR

T1 - Carbon-Carbon vs Carbon-Hydrogen Bond Activation by Ruthenium(II) and Platinum(II) in Solution

AU - van der Boom, Milko

AU - Kraatz, Heinz Bernhard

AU - Hassner, Lawrence

AU - Ben-David, Yehoshoa

AU - Milstein, David

PY - 1999/9/13

Y1 - 1999/9/13

N2 - Reaction of RuCl2(PPh3)3 with the bisphosphine {1,3,5-(CH3)3-2,6-(iPr2PCH 2)2C6H} (1) under 30 psi H2 results in quantitative C-C activation of an Ar-CH3 bond to afford Ru(Cl)-(PPh3){2,6-(iPr2PCH2) 2-3,5-(CH3)2C6H} (2) and CH4, whereas reaction of RuCl2(PPh3)3 with 1 in the presence of NaOtBu results in selective ArCH2-H bond activation to afford the benzylic complex Ru(Cl)(PPh3H{1-CH2-2,6-(iPr2PCH 2)2-3,5-(CH3)2C6H} (7). The identity of the 16-electron complex 2 was confirmed by reaction of the bisphosphine {2,6-(iPr2PCH2)2-3,5-(CH 3)2C6H2} (3), lacking the Ar-CH3 group between the phosphine arms, with RuCl2(PPh3)3. Metal insertion into an Ar-Et bond was observed as well. Follow-up of the reaction of RuHCl-(PPh3)3 with 1 by NMR and deuterium labeling studies reveal that the kinetic products of ArCH2-H bond activation (7 and H2) are irreversibly converted into the thermodynamically more stable products of Ar-C bond activation (2 and CH4) via reversal of the C-H activation process. Reaction of (COD)PtCl2 (COD = cycloocta-1,5-diene) with a stoichiometric amount of 1 at room temperature results in the exclusive formation of the benzylic Pt(II) complex Pt(Cl){1-CH2-2,6-(iPr2PCH2) 2-3,5-(CH3)2C6H} (8) and HCl. The iodide analogue of 8 has been characterized by X-ray analysis. Reaction of 8 with a 10-fold excess of HCl results in selective C-C bond activation to afford Pt(Cl){2,6-(iPr2PCH2)2-3,5-(CH 3)2C6H} (10) and MeCl. The activation parameters for the overall process are ΔH‡ = 10.6 kcal/mol, ΔS‡ = -40.1 eu, and ΔG‡(298) = 23.1 kcal/mol in a benzene/dioxane solution (5.5:1 v/v) and ΔH‡ = 2.1 kcal/mol, ΔS‡ = -65.4 eu, and ΔG‡(298) = 21.6 kcal/mol in dioxane.

AB - Reaction of RuCl2(PPh3)3 with the bisphosphine {1,3,5-(CH3)3-2,6-(iPr2PCH 2)2C6H} (1) under 30 psi H2 results in quantitative C-C activation of an Ar-CH3 bond to afford Ru(Cl)-(PPh3){2,6-(iPr2PCH2) 2-3,5-(CH3)2C6H} (2) and CH4, whereas reaction of RuCl2(PPh3)3 with 1 in the presence of NaOtBu results in selective ArCH2-H bond activation to afford the benzylic complex Ru(Cl)(PPh3H{1-CH2-2,6-(iPr2PCH 2)2-3,5-(CH3)2C6H} (7). The identity of the 16-electron complex 2 was confirmed by reaction of the bisphosphine {2,6-(iPr2PCH2)2-3,5-(CH 3)2C6H2} (3), lacking the Ar-CH3 group between the phosphine arms, with RuCl2(PPh3)3. Metal insertion into an Ar-Et bond was observed as well. Follow-up of the reaction of RuHCl-(PPh3)3 with 1 by NMR and deuterium labeling studies reveal that the kinetic products of ArCH2-H bond activation (7 and H2) are irreversibly converted into the thermodynamically more stable products of Ar-C bond activation (2 and CH4) via reversal of the C-H activation process. Reaction of (COD)PtCl2 (COD = cycloocta-1,5-diene) with a stoichiometric amount of 1 at room temperature results in the exclusive formation of the benzylic Pt(II) complex Pt(Cl){1-CH2-2,6-(iPr2PCH2) 2-3,5-(CH3)2C6H} (8) and HCl. The iodide analogue of 8 has been characterized by X-ray analysis. Reaction of 8 with a 10-fold excess of HCl results in selective C-C bond activation to afford Pt(Cl){2,6-(iPr2PCH2)2-3,5-(CH 3)2C6H} (10) and MeCl. The activation parameters for the overall process are ΔH‡ = 10.6 kcal/mol, ΔS‡ = -40.1 eu, and ΔG‡(298) = 23.1 kcal/mol in a benzene/dioxane solution (5.5:1 v/v) and ΔH‡ = 2.1 kcal/mol, ΔS‡ = -65.4 eu, and ΔG‡(298) = 21.6 kcal/mol in dioxane.

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M3 - Article

VL - 18

SP - 3873

EP - 3884

JO - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 19

ER -