16- and 18-Electron Ruthenium(II) Complexes of the Neutral, Potentially Tridentate Triamine Ligand 2,6-[Bis(dimethylamino)methyl]pyridine (NN‘N)

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Abstract

The potentially tridentate coordinating ligands NN‘N (2,6-bis[(dimethylamino)methyl]pyridine) and PNP (2,6-bis[(diphenylphosphino)methyl]pyridine) react with [RuCl2(PPh3)3] to give [mer,trans-RuCl2(NN‘N)(PPh3)] (1) and [mer,trans-RuCl2(PNP)(PPh3)] (2), respectively. Complex 1 functions as a starting material for a variety of Ru[NN‘N] complexes. It reacts with either 1 or 2 equiv of AgOTf (OTf- = SO3CF3-) to yield monocationic [RuCl(NN‘N)(PPh3)]OTf (3) and [RuOTf(NN‘N)(PPh3)]OTf (4), respectively. The molecular structure of 4 shows a pentacoordinated ruthenium(II) center with a square-pyramidal environment. The reaction of 1 with either 1 or 2 equiv of AgOTf in the presence of MeCN results in the formation of the six-coordinate mono- or dicationic complexes [mer-RuCl(MeCN)(NN‘N)(PPh3)]X (6a) (X = OTf-) and [mer,trans-Ru(MeCN)2(NN‘N)(PPh3)](OTf)2 (7), respectively. At 55 °C in acetonitrile, 1 converts quantitatively into 6b (X = Cl-) which is isostructural with 6a. Reaction of polymeric [RuCl2(nbd)]n (nbd = 2,5-norbornadiene) with NN‘N under a nitrogen atmosphere leads to the formation of neutral, dinitrogen-bridged dimeric [(μ-N2)(mer,trans-RuCl2{NN‘N})2] (8). The dinitrogen ligand is readily replaced when 8 is treated with CO, giving the neutral complex [mer,trans-RuCl2(CO)(NN‘N)] (9). The 16-electron complex 3 reacts with CO giving [mer,cis-RuCl(CO)2(NN‘N)]OTf (10), involving the formation of [RuCl(CO)(NN‘N)(PPh3)]OTf (11), followed by substitution of PPh3 by a second CO molecule. This stepwise mechanism was confirmed by the isolation of 11. The 16-electron complex 4 reacts with CO under the formation of monocationic [mer-RuOTf(CO)(NN‘N)(PPh3)]OTf (12) and a number of unidentified complexes. In the presence of ethyl alcohol, 4 reacts with CO to give monocationic [mer-RuOTf(CO)(NN‘N)(HOEt)]OTf (13). The X-ray crystal structures of 1, 4, 6a, 8, 11, and 13 are reported in abbreviated form.

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