Bikash Kumar Panda

Chemistry of a new family of aryl ruthenium species incorporating α-diimine chelation and a pendant imine-phenol function

Abstract The reaction of excess 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) with Ru(η2-RL)(PPh3)2(CO)Cl (1) has respectively furnished [Ru(η1-RL)(PPh3)2(CO)(bpy)](PF6) (2) and [Ru(η1-RL)(PPh3)2(CO)(phen)](PF6) (3) in very good yield (η2-RL is C6H2O-2-CHNHC6H4R(p)-3-Me-5, η1-RL is C6H2OH-2-CHNC6H4R(p)-3-Me-5 and R is H, Me, MeO, Cl). The chelation of bpy/phen is attended with the cleavage of RuO and RuCl bonds and iminium-phenolato→imine-phenol prototropic shift. The carbon monoxide ligand is located syn to the phenolic oxygen in 2 and 3 as opposed anti in 1. The crystal and molecular structures of [Ru(η1-HL)(PPh3)2(CO)(bpy)](PF6)·CH2Cl2 (2(H)·CH2Cl2) and [Ru(η1-ClL)(PPh3)2(CO)(phen)](PF6)·H2O (3(Cl)·H2O) are reported. In the lattice of 3(Cl)·H2O, the water molecules form dimers (O⋯O, 2.617(8) A). In the hydrogen bonded imine-phenol function the N⋯O distance is 2.550(9) A in 2(H)·CH2Cl2 and 2.581(7) A in 3(Cl)·H2O. The Rubpy fragment in 2(H)·CH2Cl2 along with the CO ligand and the metallated carbon atom define an equitorial plane from which the metallated aldimine fragment (pendant Ph excluded) is rotated by 39.1° due to interligand repulsion and the two RuP distances (2.384(3) and 2.456(3) A) become significantly different. The repulsion also counteracts the trans influence of the metallated carbanionic site, the RuN bond trans to the site being shorter. The behaviour of 3(Cl)·H2O is similar. In dichloromethane solution 2 and 3 display a quasireversible RuIII/RuII cyclic voltammetric response with E1/2 in the range 0.75–0.85 V versus SCE. The CO stretch in 2 and 3 is 30–40 cm−1 higher than that in 1 due to the presence of dπ(Ru)–pπ(bpy/phen) back-bonding. The corresponding MLCT absorption (λmax, ∼470 nm) gives rise to fluorescence (λmax, ∼540 nm). The reaction of 2-(2-pyridyl)benzthiazole (pbt) with 1 has furnished [Ru(η1-RL)(PPh3)2(CO)(pbt)](PF6) (8) in which pbt is (N,N) chelated. The properties of 8 are generally similar to those of 2 and 3.

Synthesis and structure of pyridine-2-thiolato ruthenium aryls bearing a pendant imine/phenol function

Abstract The reaction of Ru(η2-RL)(PPh3)2(CO)Cl (1) with sodium pyridine-2-thiolate (Napyt) has afforded the complexes of the type Ru(η1-RL)(PPh3)2(CO)(pyt) (3) in excellent yield (η2-RL is C6H2O-2-CHNC6H4R(p)-3-Me-5, η1-RL is C6H2OH-2-CHNC6H4R(p)-3-Me-5 and R is Me, MeO, Cl). The reaction is irreversible and is believed to proceed via cis attack by pyt− on an octahedral face. The type 3 species are thermodynamically more stable than the corresponding carboxylates, nitrites and nitrates. Structure determination of the solvate, 3(R=Cl)·C6H6·0.5C6H14 has revealed a distorted octahedral RuC2P2NS coordination sphere with the pairs (P, P), (C(aryl), N) and (C(carbonyl), S) defining the three trans directions. The η1-ClL ligand metallated ortho to the phenolic oxygen occurs in the imine–phenol tautomeric form (N⋯O, 2.639(8) A) which is consistent with IR and 1H NMR data. The transformation 1→3 is associated with changes in tautomeric form, hapticity and conformation (in relation to CO) of RL. The Ru(η1-ClL) fragment excluding the pendant C6H4Cl(p) group is nearly coplanar (dihedral angle 6.1°) with the Ru(pyt) plane. The RuS distance, 2.524(1) A, is longer than usual due to steric reasons. The type 3 complexes display a quasi-reversible Ru(III)/Ru(II) couple near 0.6 V versus SCE.

A family of thioxanthato ruthenium and osmium aryls

The title complexes of type M(RL 2 )(PPh 3 ) 2 (CO)(S 2 CSEt) (2a: M = Ru; 2b: M = Os) have been synthesized in excellent yields by reacting M(RL 1 )(PPh 3 ) 2 (CO)X (1a: M = Ru, × = Cl; 1b: M = Os, × = Br) with potassium ethyl thioxanthate and have been characterized with the help of spectral and electrochemical data. The RL 2 ligand in 2 is the imine-phenol tautomer of N-C 6 H 4 R(ρ)-4-methylsalicylaldimine (R = Me, MeO, Cl) coordinated at the carbanionic-C2 atom only while RL 1 in 1 is the iminium-phenolato tautomer chelated via carbanionic-C2 and phenolato-O atoms. The synthetic reaction is thus attended with tautomerization of the Schiff base ligand. It is also associated with a rotation of the ligand by ~180° around the M-C bond in order to exclude steric repulsion. These features have been revealed by structure determination of 2a (R = Me). The metallated aldimine ring is found to be highly noncoplanar (dihedral angle ~40°) with the thioxanthate chelate ring due to steric repulsion originating from the relatively large size of the sulfur atom. This phenomenon, which is absent in both the precursor 1 (R = Me) and in the carboxylate analogue Ru(MeL 2 )(PPh 3 ) 2 (CO)(O 2 CMe), 7, has distinctive effects on bond parameters of 2a (R = Me). Thus the two Ru-P bonds in 2a (R = Me) differ in length by as much as 0.06 A. The thioxanthate 2 is thermodynamically more stable than the precursor 1 as well as the carboxylate 7. Accordingly, both of these are irreversibly transformed to 2a (R = Me) upon treatment with thioxanthate.

Synthesis, characterization and emission properties of quinolin-8-olato chelated ruthenium organometallics

The reaction of Ru(RL1)(PPh3)2(CO)Cl,1, with quinolin-8-ol (HQ) has afforded complexes of the type [Ru(RL2)(PPh3)2(CO)(Q)],3, in excellent yield (RL1 is C6H2O-2-CHNHC6H4R(p)-3-Me-5, RL2 is C6H2OH-2-CHNC6H4R(p)-3-Me-5 and R is Me, OMe, Cl). In this process, quinolin-8-olato (Q) undergoes five-membered chelation, the iminium-phenolato function tautomerizing to the imine-phenol function. In dichloromethane solution,3 displays a quasireversible3+/3 couple near 0·50 V vs SCE (3+ is the ruthenium (III) analogue of3). Coulometrically generated solutions of3+ display a strong absorption near 395 nm associated with a shoulder near 475 nm and rhombic EPR spectra withg values near 2·55, 2·13, 1·89. Solutions of3 absorb near 415 nm and emit near 510 nm at 298 K and 585 nm at 77 K. The fluorescence is believed to originate from the3MLCT state