P-cymene Ligand Research Articles

Positioning of transition metal centres at the upper rim of cone-shaped calix[4]arenes. Filling the basket with an organometallic ruthenium unit

A series of calix[4]arenes bearing diphenylphosphino groups tethered at the upper rim have been prepared by treatment of 5,11,17,23-tetrabromo-25,26,27,28-tetrapropoxycalix[4]arene with ButLi (or BunLi) followed by reaction with PPh2Cl. The tetraphosphinated derivative 3 was found suitable for the formation of tetranuclear species, notably [3·(AuCl)4], [3·{RuCl2(p-cymene)}4], and [3·{PdCl(o-C6H4CH2NMe2)}4], all possessing an apparent C4v-symmetry in solution. Reaction of [RuCl2(p-cymene)]2 with the diphosphines 5,17-di-X-11,23-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene (X = H, 1; X = Br, 4) afforded the C2v-symmetrical dinuclear complexes [1·{RuCl2(p-cymene)}2] and [4·{RuCl2(p-cymene)}2], respectively. Reaction of the non-brominated diphosphine 1 with [PdCl(o-C6H4CH2NMe2)]2 gave the complex [1·{PdCl(o-C6H4CH2NMe2)}2]. Reaction at high dilution of [PtCl2(1,5-cyclooctadiene)] with 4 or 1 resulted in quantitative formation of the corresponding cis-chelate complexes [4·PtCl2] (12) and [1·PtCl2] (13), respectively. The trans version of 13 could also be obtained, provided that [PtCl2(PhCN)2] was used as starting complex. In the solid state, the PtCl2 unit of 12 is directed towards one bromine atom, resulting in a highly unsymmetrical calixarene structure where the metal plane is nearly parallel to the calix reference plane. The NMR spectra of 12 and 13 show an apparent C2v-symmetrical structure, suggesting a fast fan-like motion in solution of the metal plane about the P⋯P axis. Similar dynamics are likely to occur in the related cationic complexes [1·Rh(norbornadiene)]BF4 (15) and [1·Pd(Me-allyl)]BF4 (16). As shown by variable temperature studies carried out on 12 and 16, these dynamics couple with a concomitant, restricted rotation of the two PPh2 units about their coordination axis. The latter motion is probably a result of steric interactions within the phosphorus environment, two PPh rings being in competition for occupation of the cavity entrance. Reaction of the expanded cavity 5,11,17-tribromo-23-diphenylphosphino-25,26,27,28-tetrapropoxycalix[4]arene 5 with [RuCl2(p-cymene)]2 afforded the monophosphine complex [5·RuCl2(p-cymene)]. In solution as well in the solid state, the p-cymene ligand fills the calixarene basket.

Ap-cymene-ruthenium(II)–DMSO complex, [(η6-C10H14)RuCl2(DMSO)

The crystal structure of the neutral RuII complex [RuCl2(η6–C10H14)(C2H6OS)] is reported. The overall coordination geometry about the ruthenium centre is best described as a typical `piano stool'. In the p-cymene ligand, the six C atoms of the arene ring are in a planar configuration, as expected.

Synthesis and evaluation of new RuCl 2( p-cymene)(ER 2R′) and (η 1:η 6-phosphinoarene)RuCl 2 complexes as ring-opening metathesis polymerization catalysts

New RuCl 2( p-cymene)(ER 2R′) complexes (E=P, As, Sb; R, R′=H, alkyl, arylalkyl) have been synthesized and used as catalyst precursors for the ring-opening metathesis polymerization (ROMP) of cyclooctene, cyclopentene, and norbornene. When ER 2R′ was a phosphinoarene, the p-cymene ligand could be displaced upon heating and tethered (η 1:η 6-phosphinoarene)RuCl 2 complexes were obtained. Simple thermogravimetric analysis (TGA) of the complexes provided clear-cut indication on their potential catalytic activity in ROMP.

Reactivity of dinuclear arene ruthenium complexes: reactions of the hydrido complex [(p-Me-C6H4-Pri)2Ru2Cl2(μ-Cl)(μ-H)] with NaX and HX (X=F, Cl, Br, I)

The dinuclear hydrido complex [(p-Me-C6H4-Pri)2Ru2Cl2(μ-Cl)(μ-H)] (1) reacts with the sodium halides NaX in methanol to give the halogen analogues [(p-Me-C6H4-Pri)2Ru2X2(μ-X)(μ-H)] (2: X=F, 3: X=Br, 4: X=I). With HX, complex 1 reacts to give the tetrahalo complexes [(p-Me-C6H4-Pri)2Ru2X2(μ-X)2] (5: X=Cl, 6: X=Br, 7: X=I); in the case of X=I, a large excess of HI leads to the formation of the cationic complex [(p-Me-C6H4-Pri)2Ru2(μ-I)3]+ (8). The X-ray structure analysis of 1 shows a dinuclear Ru2 backbone with two terminal chloro ligands being trans with respect to each other as the two p-cymene ligands, the two bridging ligands lie in a plane perpendicular to the plane defined by the terminal chloro ligands and the ruthenium atoms.

Chemistry of Coordinatively Unsaturated Bis(thiolato)ruthenium(II) Complexes (η6-arene)Ru(SAr)2[SAr = 2,6-Dimethylbenzenethiolate, 2,4,6-Triisopropylbenzenethiolate; (SAr)2= 1,2-Benzenedithiolate; Arene = Benzene,p-Cymene, Hexamethylbenzene

Mononuclear 16-electron arene−ruthenium(II)−thiolate complexes of the general formula (η6-arene)Ru(SAr)2 (2, Ar = 2,6-C6H3Me2 = Xyl; 3, Ar = 2,4,6-C6H2(CHMe2)3; arene = C6H6 (a), arene = p-MeC6H4(CHMe2) = p-cymene (b), arene = C6Me6 (c)) have been prepared by treatment of [(η6-arene)RuCl2]2 (1) with the corresponding sodium arenethiolate in methanol. Reaction of 2b with disodium of 1,2-benzenedithiolate (=S2C6H4) led to a mixture of monomer and dimer complexes (η6-p-cymene)Ru(S2C6H4) (4b) and [(η6-p-cymene)Ru(S2C6H4)]2 (5b) in solution. A complex (η6-C6Me6)Ru(S2C6H4) (4c) was predominantly monomeric, revealed by a crystal structure analysis of 4c. All these monomeric complexes show intense blue color of the LMCT band due to the donation from the filled S(pπ) orbital to the empty Ru(dπ*) orbital, which stabilizes coordinatively unsaturated ruthenium(II). The structures of these complexes are characterized by NMR and mass spectra and elemental analysis in addition to the X-ray crystal structure determinations of 2a,b, 3c, and 4c, indicating the two-legged piano stool geometry. The newly prepared 16-electron complexes react with π-accepting molecules such as isocyanide, carbon monoxide, and trialkylphosphine. Treatment of 2b with an excess of tert-butyl isocyanide resulted in the release of the p-cymene ligand to give trans-Ru(SXyl)2(CNtBu)4 (8). Similarly, reaction of 5b with an excess of tert-butyl isocyanide afforded cis-Ru(S2C6H4)(CNtBu)4 (10), while reaction of 5b with 6 equiv of tert-butyl isocyanide gave a binuclear complex [Ru(S2C6H4)(CNtBu)3]2 (11). In the case of more strongly coordinating C6Me6 derivatives 2c and 4c, one molecule of tert-butyl isocyanide can coordinate to the ruthenium atom, resulting in the formation of (η6-C6Me6)Ru(SXyl)2(CNtBu) (9c) and (η6-C6Me6)Ru(S2C6H4)(CNtBu) (12c), respectively. Reactions of 5b and 4c with an excess of triethylphosphine afforded (η6-p-cymene)Ru(S2C6H4)(PEt3) (13b) and (η6-C6Me6)Ru(S2C6H4)(PEt3) (13c), respectively. In the carbonylation, 2b gave a binuclear carbonyl complex (CO)3Ru(μ-SXyl)3Ru(CO)2(SXyl) (14), while the carbonylation of the C6Me6 complex 2c afforded (η6-C6Me6)Ru(SXyl)2(CO) (15). Versatile reactivity of 16-electron ruthenium(II) thiolate complexes is thus demonstrated.