Ionic and Neutral Half‐Sandwich Guanidinatoruthenium(II) Complexes and Their Solution Behavior

Abstract

Ionic and neutral half‐sandwich guanidinatoruthenium(II) complexes [(η6‐C10H14)RuL(κ2(N,N′){(ArN)2C‐N(H)Ar})][OTf] [Ar = 4‐MeC6H4, L = 2‐methylimidazole (1); Ar = 2‐MeC6H4, L = 1,3,5‐triaza‐7‐phosphaadamantane (PTA; 2)], [(ArNH)3C][(η6‐C10H14)RuCl3] [Ar = 2‐ClC6H4 (3)] and [(η6‐C10H14)RuCl(κ2(N,N′){(ArN)2C‐N(H)Ar})] [Ar = 2‐ClC6H4 (4), 2‐FC6H4 (5), 4‐ClC6H4 (6), and 4‐(NO2)C6H4 (7)] have been isolated and the molecular structures of all but 6 were determined by single‐crystal X‐ray diffraction. VT 31P{1H} NMR spectroscopy of complex 2 revealed the presence of a mixture of four isomers in a ratio of appproximately 1.4:11.0:1.6:0.1. Theoretical calculations were performed on the syn‐syn, syn‐anti, anti‐syn, and anti‐anti conformers of 2, which revealed syn‐anti to be the most stable conformer, both in the gas phase and in solution. Furthermore, the energies relating to the interactions between the lone pairs of the nitrogen atoms of the CN3 unit and the antibonding orbital of the central carbon atom in the syn‐anti conformer of 2 were investigated by NBO analysis. The 1H NMR spectrum of 3 reveals the presence of two species and their ratio is dependent upon the concentration of 3 in CDCl3 and on the amount of D2O in CD3CN. The two species have been ascribed to the presence of a monomer and a water‐bridged dimer. The new complexes 1–7 were screened as pre‐catalysts in the transfer hydrogenation of acetophenone and complex 3 was tested as a pre‐catalyst in the transfer hydrogenation of a variety of ketones to explore the scope of the reaction.

Half Sandwich Electron Deficient N,N′,N′′‐Triarylguanidinatoruthenium(II) Complexes: Syntheses, Reactivity Studies, and Structural Aspects

“…The three solution species are assigned to any three isomers from syn ‐ syn, syn ‐ anti, anti ‐ syn , and anti ‐ anti isomers, most likely to the former three isomers (see Experimental section and Figure S1 in the SI). The formation of syn ‐ anti and anti ‐ syn isomers from syn ‐ syn isomer which is observed in solid state is likely due to guanidine centered rearrangement in solution involving an acyclic intermediate as previosusly discussed by two of us . VT 1 H NMR spectra of previously known complex 12 revealed the presence of three species in solution and these species were suggested to arise from the restricted N 2 C‐N(H)Ar single bond rotation yielding syn ‐ syn, syn ‐ syn a and syn ‐ syn b rotamers .…”

“…Numerous guanidinatoruthenium(II) complexes of symmetrical N , N′ , N′′ ‐triphenylguanidine, [(PhNH) 2 C=NPh] have been prepared and stucturually characterized . Subsequently, half sandwich guanidinatoruthenium(II)‐, rhodium(III)‐ and iridium(III) complexes of symmetrical N , N′ , N′′ ‐triarylguanidines, [(ArNH) 2 C=NAr] were prepared by us and others with the objectives aimed at understanding their structures in solid state and in solution and to further understand their utility as catalysts in base free and base assisted transfer hydrogenation reactions …”

Syntheses, characterisation, and catalytic role of (η5-C5Me5)Rh(iii) guanidinato complexes in transfer hydrogenation (TH) and TH–etherification

“…exo and angle sums around the N atoms ( P N) can be used to understand the degree of interaction of the N lone pair with the antibonding p-orbital of the C in the CN 3 unit of the guanidinato ligand. 19 The values of D CN and D CN 0 are comparable within 3 s cut off in 1 and 4-8 while in 2 and 3$MeOH, the value of D CN is smaller than the value of D CN 0 . Three resonance forms are possible for guanidinate ligand in metal guanidinate complexes (see Chart 3).…”

“…S3 in the ESI †). 18,19 Thus, guanidinato ligands in 1, 4 and 6 revealed synsyn conformation. The position of the chloro ligand in 4 is occupied by MeCN in 8 with SbF 6 À as the counter anion in the latter.…”

“…5a,13 Sym N,N 0 ,N 00 -trisubstituted guanidines, (RNH) 2 C]NR (Sym ¼ symmetrical; R ¼ alkyl and aryl) are one of the interesting classes of N-donor ligands due to not only their ability to act as monoanion, [R(H)N-C(NR) 2 ] À (guanidinate(1À) or guanidinato) and dianion, [C(NR) 3 ] À (guanidinate(2À)) but also the ready tunability of the R group so that distinct donor characteristics and coordination modes can be realised for these anions in their metal complexes. 16,17 In our previous publications, 18,19 we studied structural aspects and the utility of half sandwich (h 6 -pcymene)Ru(II) complexes that contain guanidinate ligand or guanidinium cation in TH of carbonyl compounds. Herein, we report syntheses and characterisation of half sandwich (h 5 -Cp*) M(III) guanidinato complexes, 1-8 by analytical, spectroscopic (IR and NMR) techniques and single crystal X-ray diffraction (SCXRD; see Charts 1 and 2).…”