Ruthenium(II) pentamethylcyclopentadienyl half-sandwich carbene complexes with polypyridyl ligands

https://doi.org/10.1016/j.jorganchem.2017.07.022Get rights and content

Highlights

  • Synthesis of half-sandwich polypyridyl complexes of ruthenium.

  • Reaction with diazoalkanes affording carbene derivatives.

  • Synthesis of acetylide derivatives of ruthenium.

  • Comparative DFT studies of the formation of metallacarbenes.

Abstract

Polypyridyl complexes [RuCl(η5-C5Me5)(N–N)] (14) [N–N double bond 2,2′-bipyridine (bpy) (1), 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me2bpy) (2), 1,10-phenanthroline (phen) (3) and 4,7-dimethyl-1,10-phenanthroline (4,7-Me2phen) (4)] were prepared by reacting [RuCl25-C5Me5)]2 with Zn dust in the presence of polypyridyl ligands. Unlike the related [RuCl(η5-C5Me5)(L1)(L2)]+ [L1, L2 = P(OR)3, PPh3] derivatives with P-donor ligands, treatment of chloro compounds 14 with diazoalkanes Ar1Ar2CN2 afforded polypyridyl carbene complexes [Ru(η5-C5Me5)(double bondCAr1Ar2)(N–N)]BPh4 (58) [Ar1 = Ar2 = Ph (a), Ar1 = Ph, Ar2 = p-tolyl (b)]. Comparative DFT studies of the formation of metallacarbenes from aromatic diazoalkanes are reported. Phosphite complex [Ru(η5-C5Me5)(bpy){P(OEt)3}]BPh4 (9) and acetylide derivatives [Ru(η5-C5Me5)(Ctriple bondCAr)(bpy)] (10, 11) [Ar = Ph (10), p-tolyl (11)] were also obtained by substitution of the carbene in 58. Unstable vinylidene cations [Ru(η5-C5Me5){double bondCdouble bondC(H)Ar](bpy)]+ (12, 13) were formed by protonation with HBF4•Et2O of acetylide species 10, 11. The complexes were characterized spectroscopically (IR and 1H, 13C, 31P NMR) and by X-ray crystal structure determination of [Ru(η5-C5Me5){double bondC(Ph)(p-tolyl)}(bpy)]BPh4 (5b).

Graphical abstract

The reaction of half-sandwich polypyridyl chloro complexes with diazoalkanes, affording carbene derivatives, is described.

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Introduction

Diazoalkanes Ar1Ar2CN2 are a class of molecules which may behave as ligands in transition metal chemistry, giving rise to a number of stable and isolable complexes [1], [2], [3], [4]. In some cases, diazoalkanes are also reported to react with metal complexes to give metallacarbene derivatives [5](a), [5](b), [5](c), [5](d), [5](e), [5](f), [5](g), [5](h), [5](i), [5](j), [6] after loss of N2.

We have a long-standing interest in the chemistry of transition metal complexes containing diazoalkanes as ligands [7], [8] and have reported the synthesis of half-sandwich derivatives [7](c), [7](d), [7](e), [7](f), [8](a), [8](b) with Cp, Cp*, indenyl and Tp of the types [Ru(η5-C5Me5)(N2CAr1Ar2){P(OR)3}(PPh3)]BPh4, [Ru(η5-C5Me5)(N2CAr1Ar2){P(OR)3}L]BPh4, [Ru(η5-C9H7)(N2CAr1Ar2){P(OR)3}L]BPh4 and [Ru(Tp)(N2CAr1Ar2){P(OR)3}L]BPh4 [L = P(OR)3 or PPh3], containing phosphites and phosphine as supporting ligands. The interesting reactivity shown by these complexes, involving (3 + 2) cycloaddition of the coordinated diazoalkane [7](c), [7](d), [8](a), [8](b) with alkene and alkyne, and hydrolysis of the [M]-N2CAr1Ar2 group to afford η2-diazene species [7](e), [7](f), prompted us to extend study by introducing different ligands such as polypyridyls into the chemistry of half-sandwich Ru(II) derivatives, with the aim of testing how they can change the reactivity of the complexes toward diazoalkanes.

Our results, which involve the synthesis of the first half-sandwich carbene complexes of ruthenium stabilized by polypyridyl ligands, are reported here.

Section snippets

General comments

All synthetic work was carried out under Ar or N2, with standard Schlenk techniques or in an inert atmosphere dry-box. All solvents were dried over appropriate drying agents, degased on a vacuum line, and distilled into vacuum-tight storage flasks. RuCl3•3H2O (Pressure Chemical Co., USA) and pentamethylcyclopentadiene C5Me5H (STREM) were used as received. The phosphites P(OMe)3 and P(OEt)3 (Aldrich) were used as received, whereas phenyldiethoxyphosphine PPh(OEt)2 was prepared by the method of

Results and discussion

Polypyridyl half-sandwich chloro complexes [RuCl(η5-C5Me5)(N–N)] (14) were prepared by reacting the dimeric compound [RuCl25-C5Me5)]2 with zinc dust in THF, in the presence of one equivalent of bidentate ligand N–N, as shown in Scheme 1. The reaction proceeeds with reduction of the central metal to Ru(II), cleavage of the dimer and coordination of the polypyridyl, affording final complexes 14 in good yields.

Chloro compounds [RuCl(η5-C5Me5)(N–N)] react with diazoalkanes Ar1Ar2CN2 in the

Conclusions

In contrast with our previous results on half-sandwich complexes containing phosphine ligands, we report here different results concerning the reaction with diazoalkanes of half-sandwich compounds containing polypyridyl ligands affording carbene derivatives [Ru(η5-C5Me5)(double bond;CAr1Ar2)(N-N)]BPh4. Acetylide compounds [Ru(η5-C5Me5)(Ctriple bondCAr)(N-N)] and unstable vinylidene cations [Ru(η5-C5Me5){double bondCdouble bondC(H)Ar)}(N-N)]+ with the pentamethylcyclopentadienyl fragment were also obtained.

Supporting information available

Computational data (Cartesian coordinates and energy values as sums of electronic energy and nuclear repulsion): .xyz file; CCDC 1538721 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgments

Thanks go to Mrs. Daniela Baldan, from the Università Ca’ Foscari Venezia (Italy), for technical assistance.

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