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Reaction of 2-imidazolyl-5,7-dimethyl-1,8-naphthyridine (L1) with [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) affords the dinuclear complex [Rh(COD)Cl]2(μ-L1) (1). Elimination of chloride from the metal coordination sphere leads to a self-assembled tetranuclear macrocycle [Rh(COD)L1]4[ClO4]4 (2). A subtle alteration in the ligand framework results in the polymeric chain compound {Rh(COD)(L2)}n(PF6)n (3) (L2 = 2-imidazolyl-3-phenyl-1,8-naphthyridine). In all these complexes, the imidazole nitrogen and one of the naphthyridine nitrogen (away from the imidazole substituent) bind the metal. The 'parallel' and 'perpendicular' dispositions of nitrogens are observed in these compounds contributing to different Rh⋯Rh separations. The L1 ligand adopts planar configuration, whereas the naphthyridine-imidazole rings deviate from planarity in L2 yielding a polymeric structure. The extent of deviation is less in the polymeric structure {Mo2(OAc) 4(L2)}n (4) in which the ligand exhibits weak axial interactions to the metal. © 2011 Elsevier B.V. All rights reserved.

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Department of Chemistry

School of Advanced Sciences

Vellore Campus

Inorganica Chimica Acta

Naphthyridine-imidazole hybrid ligands for the construction of multinuclear architecture

Site-directed anchoring of naphthyridine-functionalized N-heterocylic carbene (NHC) is achieved on a metal-metal singly bonded diruthenium(I) platform. Room-temperature treatment of 1-isopropyl-3-(5,7-dimethyl-1,8- naphthyrid-2-yl)imidazolium bromide (PINA·HBr) with Ru 2(CH3COO)2(CO)4 in acetonitrile affords the unsupported compound Ru2(CO) 4(μ2C2,N1-PIN)2Br 2 (1). Judicious alteration in the NHC ligand resulted in the bridged compound Ru2(CO)4(CH3COO)(μ2- μ2C2,N1-BIN)Br (2) (BIN = 1-benzyl-3-(3-phenyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene). X-ray analysis revealed the chelate binding of PIN on each ruthenium at equatorial sites for 1, and the bridge-chelate binding of BIN spanning the diruthenium core for 2. The catalytic utilities of the BArF (tetrakis(3,5-bis(trifluoromethyl) phenyl)borate) salts of these compounds are evaluated toward carbene-transfer reactions from ethyl diazoacetate including aldehyde olefination, cyclopropanation, and X-H (X = O, N) insertions. 1-BArF is clearly shown to be the superior catalyst. DFT calculations are undertaken to understand the influence of NHC binding on the electronic structures of the "Ru 2(CO)4" core and to rationalize the lower activity of 2-BArF. © 2011 American Chemical Society.

Organometallics

Site-directed anchoring of an N-heterocyclic carbene on a dimetal platform: Evaluation of a pair of diruthenium(i) catalysts for carbene-transfer reactions from ethyl diazoacetate

The complete sequence of reactions in the base-promoted reduction of [{RuII(CO)3Cl2}2] to [RuI 2 (CO)4]2+ has been unraveled. Several μ-OH, μ:k2-CO2H-bridged diruthenium(II) complexes have been synthesized; they are the direct results of the nucleophilic activation of metal-coordinated carbonyls by hydroxides. The isolated compounds are [Ru2(CO) 4(μ:k2-C,O-CO2H) 2(μ-OH)(NPF-Am) 2][PF6] (1; NPF-Am=2-amino-5,7-trifluoromethyl- 1,8-naphthyridine) and [Ru 2 (CO) 4(μ:k2- C,O-CO2H)(μ-OH) (NP-Me2)2][BF4]2 (2), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru4(CO) 8(H2O) 2(μ3- OH)2(μ:k2-C,O-CO2H) 4][CF3SO3]2 (3) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a pdonor chlorido ligand, which results in [Ru2(CO)4(μ:k2-C,O-CO 2H) 2(μ-Cl)- (NP-PhOMe)2][BF4] (4). The production of [Ru2(CO)4]2+ has been attributed to the thermally induced decarboxylation of a bis(hydroxycarbonyl)- diruthenium( II) complex to a dihydrido- diruthenium(II) species, followed by dinuclear reductive elimination of molecular hydrogen with the concomitant formation of the RuI-RuI single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru 2(CO)4(CH3CN)6]2+ precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by TlI salts, and heating at reflux in acetonitrile for a period of four hours are the conditions for the optimal conversion. Premature quenching of the reaction resulted in the isolation of a trinuclear RuI2RuII complex [{Ru(NP-Am) 2(CO)}{Ru2(NP-Am)2(CO) 2(μ-CO) 2}(μ3:k3-C,O,O'- CO 2)][BF4]2 (6). These unprecedented diruthenium compounds are the dinuclear congeners of the water-gas shift (WGS) intermediates. The possibility of a dinuclear pathway eliminates the inherent contradiction of pH demands in the WGS catalytic cycle in an alkaline medium. A cooperative binuclear elimination could be a viable route for hydrogen production in WGS chemistry. © 2010 Wiley-VCH Verlag 2574 GmbH&amp;Co. KGaA, Weinheim.

Chemistry - A European Journal

Mapping the transformation [{RuII (CO)3Cl 2}2]→[RuI 2 (CO) 4]2+: Implications in binuclear water-gas shift chemistry

Ferrocenylamido-naphthyridine conjugates [{(5,7-dimethyl-1,8-naphthyridin-2-yl)amino}carbonyl]ferrocene (L1) and 1,1′-bis[{(5,7-dimethyl-1,8-naphthyridin-2-yl)amino}carbonyl]ferrocene (L2) have been synthesized. Reaction of L1 with [Cu(CH3CN)6][ClO4]2 affords [Cu(L1)2][ClO4]2 (1) demonstrating tridentate coordination of the ligand utilizing naphthyridine (NP) nitrogens and carbonyl oxygen. Hydroxo-bridged neutral dirhenium(I) compound [K⊂{{Re(CO)3}2(μ-OH)(Fc(CONHNP)(COover(N, -) NP))2}] (2) is reported in which the amido-NP arm of L2 chelates a ReI, and a K+ ion is encapsulated in a six-coordinate environment rendered by four NP nitrogens and two carbonyl oxygens involving all four arms of two L2 ligands. Selective and reversible binding of K+ ion by the organometallic host has been recognized from electrochemical and fluorescence experiments. Partial hydrolysis of L2 has provided a neutral metallamacrocycle [{Re(CO)3}2{Fc(CO2)(CONHNP)}2] (3) consisting of alternate Fc and Re(CO)3 units linked by carboxylate and amide-NP bridges. The rotational freedom of the ferrocenyl rings, the flexibility of the amide linker and the multi-site coordination of the ligands are demonstrated in the molecular structures of compounds 1-3. © 2009 Elsevier B.V. All rights reserved.

Journal of Organometallic Chemistry

Multi-site coordination of ferrocenylamido-naphthyridine conjugates [{(5,7-dimethyl-1,8-naphthyridin-2-yl)amino}carbonyl]ferrocene and 1,1′-bis[{(5,7-dimethyl-1,8-naphthyridin-2-yl)amino}carbonyl]ferrocene

Since the recognition of metal-hydroxycarbonyl (or, metallacarboxylic acid) as a key intermediate in water gas shift (WGS) catalysis, numerous metal complexes incorporating hydroxycarbonyl ligands have been synthesized. In this Perspective, a brief account on the chemistry of metallacarboxylic acid and metallacarboxylate is presented. Special emphasis is placed on the hydroxycarbonyl-bridged dinuclear compounds. The relevance of hydroxycarbonyl complexes in the base-assisted reduction of ruthenium carbonyls is investigated. In particular, Lavigne's synthesis of Roper's catalyst Ru(CO) 2(PPh3)3, triruthenium dodecacarbonyl Ru 3(CO)12, and Bera's mechanistic investigation on the preparation of the metal-metal singly bonded diruthenim(i) complex [Ru 2(CO)4(CH3CN)6]2+ are described in detail. These reactions involve the decarboxylation of a "[Rum(COOH)n]" species, followed by the reductive elimination of HX (X = H, Cl or OH), steps akin to WGS catalysis. The prospect of hydroxycarbonyl chemistry in the development of bimetallic catalysis is examined. © 2010 The Royal Society of Chemistry.

Dalton Transactions

Hydroxycarbonyl complexes as key intermediates in the base-assisted reduction of ruthenium carbonyls

Reaction of cis-[Mo2(OAc)2(CH3CN) 6][BF4]2 with NP-Et,Me (2-ethyl-3-methyl-1,8- naphthyridine) in acetonitrile provides trans-[Mo2(NP-Et,Me) 2(OAc)2(CH3CN)][BF4]2 (1). Partial protonation of 1 by HBF4·Et2O in acetonitrile leads to trans-[Mo2(NP-Et,Me)2(OAc)(CH 3CN)3][BF4]3 (2). In both compounds, NP-R ligands are arranged in a head-to-head (HH) fashion leaving one of the axial sites vacant. Substitution of acetonitriles by NP-Me (3-methyl-1,8- naphthyridine) in trans-[Mo2(NP-tz)2(OAc)(CH 3CN)2][BF4]3 provides trans-[Mo 2(NP-tz)2(OAc)(NP-Me)][BF4]3 (3) with retention of configuration. Fully solvated dimolybdenum(II) compound reacts with NP-NH2 to provide [Mo2(NP-NH2) 2(NP-NH)(CH3CN)2][BF4]3 (4) in which the NP-NH2 ligands are trans and arranged in a HH fashion. The deprotonated ligand (NP-NH-) binds the dimetal unit utilizing naphthyridine nitrogen and amido nitrogen. Treatment of [Mo 2(NP-tz)2(CH3CN)4][CF 3SO3]4 with bpym (2,2′-bipyrimidine) followed by crystallization in air provided an oxo complex [Mo 2(NP-tz)2(μ2-O)2(bpym) 2][CF3SO3]4 (5). Compounds 1-5 have been characterized by a variety of spectroscopic techniques and by X-ray crystallography. The reactivity pattern is rationalized based on ligand labilities and thermodynamic stabilities. © 2010 Elsevier B.V. All rights reserved.

Mixed-ligand compounds incorporating quadruply bonded dimolybdenum(II) core: Syntheses, structures and reactivity studies

The 1,8-naphthyridine - functionalized N-heterocyclic carbene 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)im;dazol-2-ylidene (BIN) has been successfully coordinated to Pd(II), W(O), Rh(I), and Ir(III), exhibiting its diverse binding modes. Reaction of BIN · HBr with Ag2O, followed by transmetalation with PdCl2(COD)2 provides a cis complex PdCl2(κC2-BIN)2 (1). Treatment of BIN·HBr with W(CO)4(piperidine)2 in acetonitrile affords a chelate complex W(CO)4(κ 2C2,N1′-BIN) (2). Reaction of {RhCI(COD)}2 with KOtBu and subsequent treatment with BIN • HBr in 1:2 and 1:1 ratio results In the mono and dinuclear complexes [Rh(COD)Br(κC2-BIN)] (3) and [{Rh(COD)Br}2(κ N8′:κC2-BIN)] (4), respectively. In complex 3, the "Rh(COD)Br" unit is coordinated to the carbene center, whereas an additional "Rh(COD)Br" unit is attached to naphthyridine nitrogen In complex 4 in an anti arrangement. Under Identical reaction condition, a novel Ir(III) complex [Ir(κ2C2,N1′BIN) (κ2C3′,C2-BIN)(H2O)Br] Br (5) has been synthesized. Complex 5 is proved to be catalytically active In hydrogen transfer reaction from IPrOH. All complexes have been characterized by spectroscopic methods and X-ray crystallography. © 2009 American Chemical Society.

Inorganic Chemistry

Multifaceted coordination of naphthyridine - Functionalized N-heterocyclic carbene: A novel "IrIII(C∧N)(C∧C)" compound and its evaluation as transfer hydrogenation catalyst

Oxidative additions of dichloromethanes to a diiridium(I) core, bridged by 2-ferrocenyl-1,8-naphthyridines (NP-Fc), provide an iridium(II) dimer, [IrCl2(CO)2(η1-NP-Fc)]2, featuring an unsupported Ir-Ir single bond (2.7121(8) Å). © The Royal Society of Chemistry.