New Rhodium Complexes Coordinated by Bidentate Imine Ligands with Benzothiazolyl Functionalities

Abstract

Dedicated to Professor Dieter Seebach on the occasion of his 65th birthdayThe pseudo-square-planar complexes [Rh(cod)(Hbbtm)]BF 4 (3), [Rh(bbte)(cod)]BF 4 (4), [Rh(CO) 2 (Hbbtm)]BF 4 (5), [Rh(bbte)(CO) 2 ]BF 4 (6), [Rh(bbtm)(cod)] (7) and [Rh(bbtm)(CO) 2 ] (8) (Hbbtm bis(benzothiazol-2-yl)methane 2,2'-methylenebis[benzothiazole], bbte bis(benzothiazol-2-yl)ethane 2,2'-(ethane-1,2-diyl)bis[benzothiazole], and cod cycloocta-1,5-diene) were synthesized and characterized. Diastereotopic protons were observed for the protons at the bridge in the 1 H-NMR of 3 and 5. Twisting of the ethane-1,2-diyl bridge in 4 and 6 effects chemical equivalence of the CH 2 groups in solution. Unusually large downfield shifts occur on coordination of the deprotonated ligand Hbbtm as the negative charge is delocalized in 7 and 8. The NMR signals of the cod ligand in 4 could be differentiated. The X-ray crystal structures of 3, 4, and 6 are reported.Introduction. ± Our interest in rhodium complexes that contain ligands similar to compounds in biological systems has been raised since the successful use of rhodium complexes with H 2 O-soluble biopolymers (human-serum albumin) as ligands in the hydroformylation of olefins [1]. Several groups have described the synthesis, characterization, and application of rhodium(I) complexes containing five-membered heterocycles in homogeneous catalytic transformations [2 ± 11].[Rh(CH 2 {mBnzim} 2 )(CO) 2 ]BPh 4 and [Rh(CH 2 {mim} 2 )(CO) 2 ]BPh 4 (mBnzim methylbenzimidazolyl and mim methylimidazolyl) have been structurally characterized [2] and used in the intramolecular hydroamination of terminal and nonterminal alkynes [3] and the cyclization of acetylenic carboxylic acids and acetylenic alcohols to afford O-containing heterocycles [4]. The methylene-bridge protons undergo exchange in deuterated solvents once the ligand is coordinated to the metal center. Accordingly, deprotonation of Hbbom (bis(2-benzoxazol-2-yl)methane) and reaction with [RhCl(CO) 2 ] 2 yielded [Rh(bbom)(CO) 2 ], but this complex proved to be a weak catalyst precursor for the reduction of nitrobenzene to aniline [5].Oro and co-workers [6] have described the synthesis and structural characterization of mononuclear and binuclear rhodium(I) complexes with the general formulae [{RhCl(CH 2 (pz) 2 )(cod)} 2 ], [Rh(CH 2 (pz) 2 )(cod)]ClO 4 and [Rh(CH 2 (pz) 2 )(CO) 2 ]ClO 4 (CH 2 (pz) 2 bis(pyrazolyl)methane). Hydroformylation of hex-1-ene and heptenes are catalysed by [Rh 2 (CO) 2 {P(OPh) 3 } 2 (m-pz) 2 ] [7] and [Rh{P(OPh) 3 } 2 (pz)] 2 [8] (pz pyrazolato) under mild conditions. Evidence that binuclear [Rh 2 Cl 2 (cod) 2 (L)] complexes that contain bidentate NN' and tridentate NN'N 1-(alkylamino)pyrazoles exist as ionic species was recently presented [10]. Substitution of a CO ligand in

A New iso-Amyl Benzothiazolyl Sulfoxide as an Extractant for Palladium and the Crystal Structure of its Palladium (II) Complex

“…The C=N stretching vibration observed at 1631 cm -1 for ABSO is shifted to 1613 cm -1 in the Pd-ABSO complex, and the shift extent is similar to the Pd(II)–imidazole complex [ 26 , 27 ]. These facts indicated that ABSO is coordinated with Pd (II) via nitrogen atom on the thiazole ring, which is similar to the binding of benzothiazole derivatives to a number of other metals reported previously [ 28 , 29 , 30 , 31 , 32 ].…”

“…Almost all C-C-C bond angles of ABSO phenyl ring are about 120°, except that the angles of C(1)-C(2)-C(3), C(4)-C(5)-C(6) are a little smaller (117.9° and 117.1°). The bond lengths and angles in the thiazole unit are essentially similar to those reported for thiazole units in [Rh{bis(benzothiazol-2-yl)ethane}(CO) 2 ]BF 4 [ 29 ], [ReOCl 3 (2-(2-pyridyl)benzthiazole)] [ 31 ], [cis-dichloro(2-pyrid-2-ylbenzothiazole)platinum(Ⅱ)] [ 32 ]. The N(1)-C(7) bond length (1.306(3) Å) are between the single and double bond (according to Pauling’s presentation, the bond lengths of C-N and C=N are 1.47 and 1.29 Å respectively [ 36 ]), which may result from the fact that the benzothiazole-2-thiolate group has the following resonance structure ( Figure 8 ) [ 37 ], namely, the negative charge of S(2) is partially delocalized to the N atom.…”

Study on Mechanism of Extraction of Palladium(II) with 2-Ethylhexyl Benzimidazole Sulfide

“…In addition, the ν(C-N) of free 2-ethylhexyl benzimidazole sulfide ligand appears as a strong absorption at 1402 cm -1 , while the characteristic ν(C-N) absorption weakens in extracted complex, which is similar to the binding of benzimidazole derivatives to a number of other metals reported previously 26,27 , indicating that 2-ethylhexyl benzimidazole sulfide is coordinated with Pd(II) via N atom on the benzimidazole ring.…”

Thione complexes of Rh(i): a first comparison with the bonding and catalytic activity of related carbene and imine compounds

“…10 Here we describe the synthesis of a series of thione complexes derived from [RhCl(cod)] 2 and [RhCl(CO) 2 ] 2 . A new group of neutral and cationic heterocyclic carbene complexes as well as neutral imine compounds are also discussed.…”

“…The corresponding cationic carbonyl complex (10) formed readily in the presence of CO. Our method differs somewhat from that of Mata et al mentioned before (see Scheme 1). 8 The binuclear rhodium complexes [RhCl(cod)] 2 and [RhCl(CO) 2 ] 2 are also readily cleaved by N-donor ligands.…”