Coordinating Tectons 4: Coordination Chemistry of the 4,5-Diazafluoren-9-yl Moiety as a Metallo-Ligand for Allenylidene Complexes

Abstract

We describe how the 4,5-diazafluoren-9-yl moiety has been utilized in the construction of multinuclear complexes incorporating a ruthenium(II) allenylidene functionality. The coordination chemistry of diazafluorenylterminated allenylidene complexes is limited by the sensitivity (instability) of the allenylidene moiety under a variety of synthetic conditions. In contrast the κ 2 -N,N′-coordination of the diazafluorenyl propargylic alcohol (alkynol) to a metal center prior to allenylidene formation provides a facile route toward the synthesis of multinuclear allenylidene coordination complexes. Our synthetic attempts and successes are discussed in combination with spectroscopic and electronic characterization of the latter cases. ■ INTRODUCTIONThere exists a fundamental interest in the properties of multimetallic molecular complexes, to afford both understanding and applications in catalysis, 1−3 molecular electronics, 4−6 photochemistry, 7,8 and combinations thereof. 9−12 Of particular interest are those complexes in which the metal sites cooperate to yield synergistic properties largely absent in mononuclear analogues. To this end, molecules in which multiple metal sites are connected by conjugated organic bridges are of particular interest, as such bridging moieties are expected to foster increased degrees of interaction between the metal sites. The synergistic effects of the metal sites may then be readily tuned via synthetic modifications to the bridging moiety or to the coordination sphere of the pendant metal sites or by changing the identity of the metal atom(s). 13 The prevalent examples of such complexes are those bearing symmetrical (oligo)ethynylene 14,15 or polypyridyl bridging ligands. 16,17 It is our goal to synthesize discrete molecular components that can be assembled into multinuclear complexes via a coordination chemistry methodology, i.e., coordinating tectons. 18−20 Specifically we seek also to develop these tectons as asymmetric components in order to provide facile synthetic access to heterometallic complexes, and thus more readily elucidate and tune the effects of a particular metal site on the molecular properties of the complex as a whole. Our lab and others have reported on transition metal σ-alkynyl complexes derived from 5-ethynyl-2,2′-bipyridine and the successful κ 2 -N,N′-complexation of additional d-and f-block metals to the pendant diimine moiety. 19,21−28 We have previously reported the synthesis and characterization of the complexes [MCl(PP) 2 (CC{4,5-diazafluoren-9-yl})]PF 6 (M = Ru, Os; PP = dmpe, dppm, dppe; not all combinations), 18 and in this investigation we describe efforts to synthesize multinuclear complexes incorporating 1, Scheme 1. Recent developments in metallocumulene chemistry have been reported. 29 Contemporary with our investigations examples of the formation of bimetallic complexes by reaction of metal precursors with the closely related allenylidene

Controlled Reactivity of Terminal Cyaphide Complexes: Isolation of the 5-Coordinate [Ru(dppe)2(C≡P)]+

“…It is, however, notable that there are no direct comparators incorporating either ethynyl or cyanide ligands in the apical site, whether at ruthenium or any other group 8 or 9 metal. Indeed, although the intermediacy of 5-coordinate ruthenium alkynyl complexes is invoked in the synthesis of bis­(alkynyl)and, indeed, cyaphide-alkynylcomplexes, relatively few discrete examples are known, while in those that are, the alkynyl (or cyano) ligand adopts a basal, rather than apical, coordination site.…”

Coordinating Tectons. Experimental and Computational Infrared Data as Tools To Identify Conformational Isomers and Explore Electronic Structures of 4-Ethynyl-2,2′-bipyridine Complexes

“…13 C{ 1 H} NMR (CDCl 3 , 126 MHz): δ 30.4 (p, PCH 2 CH 2 P), 120.8 (s, C3′), 123.6 (s, C3), 125.4 (s, C5′), 127.1 (s, C5), 127.5 (s, C meta ), 127.7 (s, C meta ), 129.5 (s, C para ), 129.6 (s, C para ), 133.7 (s, C ortho ), 134.5 (s, C ortho ), 135.1 (m, C ipso ), 137.6 s, C4′), 147.8 (s, C6), 150.4 (s, C6′), quaternary carbons (except C ipso ) were not detected. 19 [Ru(CC-4-bpy)(CO) 2 Cp] (9). [RuCl(CO) 2 Cp] (150 mg, 0.584 mmol), 1 (106 mg, 0.584 mmol), and CuI (10 mg, 10 mol %) were dissolved in a mixture of Et 3 N (25 mL) and THF (10 mL) and stirred at ambient temperature for 48 h. The solvent was removed in vacuo, and the reaction mixture was chromatographed on alumina (neutral, Brockmann activity III), with CH 2 Cl 2 /hexane (25% v/v) as eluent to remove unreacted starting materials, while a yellow band was eluted with 100% CH 2 Cl 2 .…”

“…Robust, and ideally modular, synthetic methodologies that permit ready assembly of metal-containing compounds and complexes would allow facile exploration of the chemical, physical, and optoelectronic features provided by metal complexes and design of new materials. Such modular methodologies for the construction of large heterometallic complexes which take advantage of the multiple coordination sites offered by ethynyl bipyridines was previously pursued by Lang in his “Tinkertoy” approach. − We have been recently focused on an allied approach to the construction of bimetallic complexes through the preparation of modular organometallic “coordinating tectons”. − A series of bimetallic complexes of the well-studied bifunctional ligand 5-ethynyl-2,2′-bipyridine were synthesized by this approach, and weak electronic communication was observed between two metal centers across this ligand . Indeed, the electronic interactions between metal termini separated by an organic functionality, M–bridge–M′, are often investigated in order to define the intramolecular electron transfer (or wirelike) characteristics of the assembly. − Investigations of organometallic complexes in this area have focused on the mixed-valence characteristics of bimetallic complexes derived from bridging moieties such as polyynes, − oligo­(phenylene)­ethynylenes, and bis­(terpyridine)metal complexes .…”

Selective N-Alkylation of Aminobenzenesulfonamides with Alcohols for the Synthesis of Amino-(N-alkyl)benzenesulfonamides Catalyzed by a Metal–Ligand Bifunctional Ruthenium Catalyst

“…5 ), [( p -cymene)­Ru­(bpy)­Cl] (cat. 6 ), [( p -cymene)­Ru­{6,6′-(OMe) 2 -2,2′-bpy­(H 2 O)}]­[OTf] 2 (cat. 7 ), [( p -cymene)­Ru­(6,6′-(OH) 2 bpy)­(H 2 O)]­[OTf] 2 (cat.…”

“…5), 25 [(p-cymene)Ru(bpy)Cl] (cat. 6), 26 heated in an oil bath at 125 °C for 12 h. Then, the mixture was cooled to ambient temperature, concentrated in vacuo, and purified by flash column chromatography with hexanes/ethyl acetate to afford corresponding products. 4-Amino-N-benzylbenzenesulfonamide (3aa).…”