Chemistry of [Ru(1,3-diaryltriazenide)2(PPh3)2]z (z = 0, +). a hindered RuII,IIIN2P2 family with valence-independent geometry

Menon, Mahua ; Chattopadhyay, Surajit ; Chakravorty, Animesh ; Bag, Nilkamal ; Pramanik, Amitava (1995) Chemistry of [Ru(1,3-diaryltriazenide)2(PPh3)2]z (z = 0, +). a hindered RuII,IIIN2P2 family with valence-independent geometry Inorganic Chemistry, 34 (6). pp. 1361-1367. ISSN 0020-1669

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The reaction of Ru(PPh3)3Cl2 with 1,3-diaryltriannes, (p-RC6H4N)(p-RC6H4NH)N (HRL; R = H, Me. OMe, Cl), in ethanol affords RuII(RL)2(PPh3)2], which is oxidized by cerium(IV) to the trivalent complex isolated as [RuIII(RL)2(PPh3)2]PF6. Yields are near-quantitative for both oxidation states. The X-ray structures of Ru(HL)2-(PPh3)2 and [Ru(ClL)2(PPh3)2]PF6·2CH2Cl2 have revealed centrosymmetric trans geometry for both RuN4P2 coordination spheres. The four-membered triazenide chelate rings are near-perfect planes. and the average Ru—N length decreases by ∼0.04 Å in going from the bivalent to the trivalent complex due to the contraction of the metal radius in the primarily a-bonded RuN4 frame. In contrast. the Ru—P length is ∼0.07 Å shorter in the bivalent complex because of strong Ru—P 44Π-3dΠ back-bonding, which is lacking in the trivalent complex. Studies on the energetics of models have revealed that cis geometry is precluded by severe steric crowding of triazenide vis-a-vis phosphine aryl functions. The repulsions are very strong even in the "best" rotameric configurations of triazene aryls. The bivalent complexes are diamagnetic and display an MLCT band near 500 nm. The trivalent species have one unpaired electron (1.78-1.86 µ8). and they show a strong band near 1200 nm which has been assigned to LMCT excitation (au→ag, bg) on the basis of model EHMO results. The E½ values of the stereoretentive ruthenium(III)—ruthenium(II) couple lie in the range 0.08-0.37 V vs SCE. increasing in the order OMe < Me < H < Cl. Crystal data for the complexes arc as follows: Ru(HL)2(PPh3)2, crystal system triclinic. space group P1; a = 10.964(6) Å, b = 11.821(7) Å, c = 21.183(9) Å, a = 76.52(4)°. β= 78.17(4)°, y = 71.18(4)°, V = 2502(2) Å3, Z = 2, R = 3.93%. Rw = 4.32%; [Ru(ClL)2(PPh3)2(PF6CH2Cl2, crystal system triclinic; space group Pl, a = 11.093(6) Å, b = 12.386(4) Å, c 13.757(6) Å, a = 104.11(3)°, β= 103.48(4)°, y = 110.57(3)'. V = 1607(1) Å3, Z = I. R = 5.00%,Rw= 5.64%.

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