Copper(I) Complexes of Amide Functionalized Bisphosphine: Proximity Enhanced Metal-Ligand Cooperativity and Its Catalytic Advantage in C(sp3)-H Bond Activation of Unactivated Cycloalkanes in Dehydrogenative Carboxylation Reactions.

The reactions of amide functionalized bisphosphine, o-Ph2PC6H4C-(O)N(H)C6H4PPh2-o (1) (BalaHariPhos), with copper salts is described. Treatment of 1 with CuX in a 1:1 molar ratio yielded chelate complexes of the type [CuX{(o-Ph2PC6H4C(O)N(H)C6H4PPh2-o)}-κ2-P,P] (X = Cl, 2; Br, 3; and I, 4), which on subsequent treatment with KOtBu resulted in a dimeric complex [Cu(o-Ph2PC6H4C(O)(N)C6H4PPh2-o)]2 (5). Interestingly, complexes 2-4 showed weak N-H···Cu interactions. These weak H-bonding interactions are studied in detail both experimentally and computationally. Also, CuI complexes 2-5 were employed in the oxidative dehydrogenative carboxylation (ODC) of unactivated cycloalkanes in the presence of carboxylic acids to form the corresponding allylic esters. Among complexes 2-5, halide-free dimeric CuI complex 5 showed excellent metal-ligand cooperativity in the oxidative dehydrogenative carboxylation (ODC) in the presence of carboxylic acids to form the corresponding allylic esters through C(sp3)-H bond activation of unactivated cycloalkanes. Mechanistic details of the catalytic process were established by isolating the precatalyst [Cu{(o-Ph2PC6H4C(O)(NH)C6H4PPh2-o)-κ2-P,P}(OOCPh)] (6) and fully characterized by mass spectrometry, NMR data, and single-crystal X-ray analysis. Density functional theory-based calculations further provided a quantitative understanding of the energetics of a series of H atom transfer steps occurring in the catalytic cycle.

A greener approach towards the synthesis of N-heterocyclic thiones and selones using the mechanochemical technique.

This manuscript describes the synthesis of N-heterocyclic thiones and selones of a variety of imidazolium salts involving an eco-friendly and solventless ball-milling technique. The products have been isolated in almost quantitative yield, involving a minimum quantity of solvents only for the isolation of products by column chromatography, and in some cases for purification purposes. Both mono- and bisimidazolium salts afforded N-heterocyclic thiones and selones. The methodology is found to be superior in terms of reaction time, yield and energy efficiency as compared to conventional solution-state reactions.

RuII complexes of 1,2,3-triazole appended tertiary phosphines, [P(Ph){(o-C6H4)(1,2,3-N3C(Ph)CH}2] and [P(Ph){o-C6H4(CCH)-(1,2,3-N3-Ph)}2]: highly active catalysts for transfer hydrogenation of carbonyl/nitro compounds and for α-alkylation of ketones.

The synthesis of two new 1,2,3-triazole appended monophosphines [P(Ph){(o-C6H4)(1,2,3-N3C(Ph)CH}2] (1) and [P(Ph){o-C6H4(CCH)(1,2,3-N3-Ph)}2] (2) and their RuII complexes is described. The reactions of 1 and 2 with [Ru(PPh3)3Cl2] in a 1 : 1 molar ratio produced cationic complexes 3 and 4, respectively. Both the complexes showed very high catalytic activity towards transfer hydrogenation, nitro reduction, and α-alkylation reactions and afforded the corresponding products in good to excellent yields. The free energy of ß-hydride elimination from the respective Ru-alkoxide intermediates, a key mechanistic step common to all the three catalytic pathways, was calculated to be close to ergoneutral by density functional theory-based calculations, which is posited to rationalize the catalytic activity of 3. The reduction of aromatic nitro compounds was found to be highly chemoselective and produced the corresponding amines as major products even in the presence of a carbonyl group. The triazolyl-N2 coordinated RuII-NPN complex 3 showed better catalytic activity compared to the triazolyl-N3 coordinated complex 4.

1,2,3-Triazole based ligands with phosphine and pyridine functionalities: synthesis, PdII and PtII chemistry and catalytic studies.

This manuscript describes the syntheses of pyridine appended triazole-based mono- and bisphosphines, [o-Ph2P(C6H4){1,2,3-N3C(Py)C(H)}] (2), [o-Br(C6H4){1,2,3-N3C(Py)C(PPh2)}] (3), [C6H5{1,2,3-N3C(Py)C(PPh2)}] (4), [Ph2P(C6H4){1,2,3-N3C(Py)C(PPh2)}] (5) and [3-Ph2P-2-{1,2,3-N3C(Ph)C(PPh2)}C5H3N] (6), their palladium and platinum chemistry and catalytic applications. These ligands upon treatment with [M(COD)Cl2] (M = Pd or Pt) yielded complexes with different coordination modes, depending on the reaction conditions. Both κ2-P,N and κ2-P,P coordination modes were observed in many of the complexes indicating the ambidentate nature of these ligands. Monophosphine 2 in the presence of a base afforded rare fused-5,6-membered PCN pincer complexes [MCl{o-Ph2P(C6H4){1,2,3-N3C(Py)C(H)}}-κ3-P,C,N] (7, M = Pd; 8, M = Pt), whereas the reactions of 4 with [M(COD)Cl2] (M = Pd, Pt) produced κ2-P,N chelate complexes [MCl2{C6H5{1,2,3-N3C(Py)C(PPh2)}-κ2-P,N}] (9, M = Pd; 10, M = Pt). Similar reactions of 5 and 6 resulted in κ2-P,P chelate complexes [MCl2{{3-Ph2P-2-{1,2,3-N3C(Ph)C(PPh2)}C5H3N}-κ2-P,P}] (11, M = Pd; 12, M = Pt) and [MCl2{3-Ph2P-2-{1,2,3-N3C(Ph)C(PPh2)}C5H3N}-κ2-P,P}] (13, M = Pd; 14, M = Pt), respectively. The palladium(II) complexes have shown excellent catalytic activity in the α-alkylation reaction of acetophenone derivatives.

Platinum Assisted Tandem P-C Bond Cleavage and P-N Bond Formation in Amide Functionalized Bisphosphine o-Ph2PC6H4C(O)N(H)C6H4PPh2-o: Synthesis, Mechanistic, and Catalytic Studies.

The reactions of amide functionalized bisphosphine o-Ph2PC6H4C(O)N(H)C6H4PPh2-o (1) with platinum salts are described. Treatment of 1 with [Pt(COD)Cl2] yielded a chelate complex, [PtCl2{o-Ph2PC6H4C(O)N(H)C6H4PPh2-o}κ2-P,P] (2), which on subsequent treatment with LiHMDS formed a novel 1,2-azaphospholene-phosphine complex [Pt(C6H5)Cl{o-C6H4{C(O)N(o-PPh2(C6H4))P(Ph)}}κ2-P,P] (3) involving a tandem P-C bond cleavage and P-N bond formation. The same complex 3 on passing dry HCl gas afforded the dichloro complex [PtCl2{o-C6H4{C(O)N(o-PPh2(C6H4))P(Ph)}}κ2-P,P] (5). Complex 2 upon refluxing in toluene or treatment of 1 with [Pt(COD)Cl2] in the presence of a base at room temperature resulted in the pincer complex [PtCl{o-Ph2PC6H4C(O)N(C6H4PPh2-o)}κ3-P,N,P] (4). Reaction of 1 with [Pt(COD)ClMe] at room temperature also afforded the pincer complex [PtMe{o-Ph2PC6H4C(O)N(C6H4PPh2-o)}κ3-P,N,P] (6). Mechanistic studies on 1,2-azaphospholene formation showed the reductive elimination of LiCl to form a phosphonium salt that readily adds one of the P-C bonds oxidatively to the in situ generated Pt0 species to form a chelate complex 3. The analogous palladium complex [PdCl2{o-C6H4{C(O)N(o-PPh2(C6H4))P(Ph)}}κ2-P,P] (7) showed excellent catalytic activity toward N-alkylation of amines with alcohols with a very low catalyst loading (0.05 mol %), and the methodology is very efficient toward the gram-scale synthesis of many N-alkylated amines.

Synthesis, structural, characterization and Hirshfeld analysis of a bisselenide and a zinc complex of a new hemilabile ferrocenylbisphosphane, [Fe{C5H4P(C6H4CH2NMe2-o)2}2].

The novel hemilabile ferrocenylbisphosphane 1,1'-bis(bis{2-[(dimethylamino)methyl]phenyl}phosphanyl)ferrocene, [Fe{C5H4P(C6H4CH2NMe2-o)2}2] (1), was synthesized by reacting bis(dichlorophosphanyl)ferrocene, [Fe{C5H4(PCl2)}2] with LiC6H4CH2NMe2-o. Treatment of 1 with gray selenium and anhydrous ZnCl2 yielded, respectively, the bisselenide (ferrocene-1,1'-diyl)bis(bis{2-[(dimethylamino)methyl]phenyl}phosphine selenide), [Fe(C23H28N2PSe)2] (2), and the dizinc complex [µ-1,1'-bis(bis{2-[(dimethylamino)methyl]phenyl}phosphanyl)ferrocene-κ2N,P:κ2N',P']bis[dichloridozinc(II)] dichloromethane monosolvate, [FeZn2Cl4(C23H28N2P)2]·CH2Cl2 (3), and both have been structurally characterized. Both compounds crystallized with the asymmetric unit containing half a molecule and with the Fe atom on an inversion centre. A Hirshfeld surface analysis indicated that the most significant contributions to the crystal packing of 2 are from H...H (76.7%), C...H/H...C (13.2%) and Se...H/H...Se (7.1%) contacts, while those for 3 are from H...H (62.3%), Cl...H/H...Cl (24.4%) and C...H/H...C (10.9%) contacts.

Group 11 metal complexes of the dinucleating triazole appended bisphosphine 1,4-bis(5-(diisopropylphosphaneyl)-1-phenyl-1H-1,2,3-triazol-4-yl)benzene.

The synthesis of a triazole appended dinucleating bisphosphine 1,4-bis(5-(diisopropylphosphaneyl)-1-phenyl-1H-1,2,3-triazol-4-yl)benzene (2) and its coinage metal complexes are described. The dinucleating bisphosphine 2 was obtained by the temperature-controlled lithiation of 1,4-bis(1-phenyl-1H-1,2,3-triazol-4-yl)benzene (1a) and 1,4-bis(1-(2-bromophenyl)-1H-1,2,3-triazol-4-yl)benzene (1b) followed by the reaction with iPr2PCl. The reactions of 2 with copper(I) halides in 1 : 2 molar ratios yielded the [Cu(µ2-X)]2 dimeric complexes [{Cu(µ2-X)}2(PiPr2N3PhC2)2C6H4] (3, X = Cl; 4, X = Br; and 5, X = I), whereas the reaction of 2 with AgBr resulted in the formation of hetero-cubane complex [{Ag4(µ3-Br)4}{(PiPr2N3PhC2)2C6H4}2] (7). Similar reactions of 2 with AgX in 1 : 2 molar ratios yielded disilver complexes [{Ag(µ2-X)}2{(PiPr2N3PhC2)2C6H4}] (6, X = Cl and 8, X = I). Treatment of 2 with AgOAc in a 1 : 2 molar ratio afforded a dinuclear complex [Ag2(µ2-OAc)2{(PiPr2N3PhC2)2(C6H4)}] (9) with one of the acetate ligands bridging the two metal centres in the side-on mode, whereas the other one adopting the end-on mode keeping the >CO group uncoordinated. The reaction of 2 with two equivalents of [AuCl(SMe2)] afforded the digold complex [(AuClPiPr2N3PhC2)2C6H4] (10). The molecular structures of 2-5 and 7-10 were confirmed by single crystal X-ray analysis. Non-covalent interactions between Cu and Carene were observed in the molecular structures of 3, 4 and 5. These weak interactions were also assessed by DFT calculations in terms of their non-covalent interaction plots (NCI) and QTAIM analyses.

Novel approach to benzo-fused 1,2-azaphospholene involving a Pd(II)-assisted tandem P-C bond cleavage and P-N bond formation reaction.

New bisphosphine o-Ph2PC6H4C(O)N(H)C6H4PPh2-o (1) (Bala-HariPhos) showed a unique reactivity towards Pd(ii) resulting in a 1,2-azaphospholene complex, involving a tandem P-C bond cleavage, P-N bond formation and cyclization process via the elimination of PhH. Mechanistic details were investigated using NMR spectroscopy, DFT calculations and kinetic data, and by SCXRD analysis. It involves the reductive elimination from a tautomerised complex to form a phosphonium salt followed by oxidative addition.

Rare Au···H Interactions in Gold(I) Complexes of Bulky Phosphines Derived from 2,6-Dibenzhydryl-4-methylphenyl Core.

Gold(I) complexes of sterically demanding phosphines derived from 2,6-dibenzhydryl-4-methylphenyl core viz: 2,6-dibenzhydryl-N,N-bis((diphenylphosphane)-methyl)-4-methylaniline (1), (2,6-dibenzhydryl-4-methylphenyl)-diphenylphosphane (2), N-(2,6-dibenzhydryl-4-methylphenyl)-1,1-diphenylphosphanamine (3), and (2,6-dibenzhydryl-4-methylphenoxy)-diphenylphosphane (4) are described. The reaction of 1 with 2 equiv of [AuCl(SMe2)] in dichloromethane yielded [{AuCl}2{Ar*N(CH2PPh2)2}] (5), which on further treatment with 2 equiv of AgSbF6 and 1 equiv of 1 produced 12-membered dimeric complex [Au2{µ-(Ar*N(CH2PPh2)2)2}][(SbF6)2] (6). A similar reaction of 5 with AgSbF6 in CH3CN afforded [{Au(NCCH3)}2{Ar*N(CH2PPh2)2}][(SbF6)2] (7). Equimolar reactions of bulky phosphines 2, 3, and 4 with [AuCl(SMe2)] resulted in [AuCl(PPh2Ar*)] (8), [AuCl(PPh2NHAr*)] (9), and [AuCl(PPh2OAr*)] (10). Complexes 9 and 10 on treatment with AgSbF6 in CH3CN produced the cationic complexes [Au(NCCH3)(PPh2NHAr*)][(SbF6)] (11) and [Au(NCCH3)(PPh2OAr*)][(SbF6)] (12), respectively. The molecular structure of complex 6 revealed the presence of a strong intramolecular aurophilic interaction with a Au···Au distance of 2.9720(4) Å. Careful analysis of molecular structure of 5 revealed the presence of rare Au···H-C (sp3) interactions between the gold(I) atom and one of the methylene protons of -NCH2PPh2 groups. The solution 1H NMR signals of the methylene protons of 5 showed a considerable downfield shift (∼1 ppm) compared to that of the free ligand indicating their interactions (Au···H) with the Au atom. Complexes 8 and 10 also showed Au···H interactions in their molecular structures. The existence of the Au···H interaction was studied by variable temperature 1H NMR data in the case of complex 5 and further evinced by the QTAIM analysis in complexes 5, 8, and 10.

New 1,2,3-triazole based bis- and trisphosphine ligands: synthesis, transition metal chemistry and catalytic studies.

The syntheses and transition metal chemistry of triazole-based bis- and tris-phosphines, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (2), 5-(diphenylphosphanyl)-4-(2-(diphenylphosphanyl)phenyl)-1-phenyl-1H-1,2,3-triazole (5), 1,4-bis(2-(diphenylphosphanyl)phenyl)-1H-1,2,3-triazole (6) and 5-(diphenylphosphanyl)-1,4-bis(2-(diphenylphosphanyl)phenyl)-1H-1,2,3-triazole (7), are described. Bisphosphines 5 and 6 show versatile coordination behavior due to the presence of at least four donor atoms. The reactions of 5 and 6 with group VI metal carbonyl derivatives were found to be highly sensitive to the reaction conditions. Bisphosphine 5 upon treatment with [M(CO)4(piperidine)2] (M = Mo and W) yielded both P,P and P,N coordinated complexes [M(CO)4(5)] [M = Mo-κ2-P,N (8); W-κ2-P,N (9); Mo-κ2-P,P (10); W-κ2-P,P (11)], whereas 6 afforded only P,N coordinated complexes [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))CH}-κ2-P,N}Mo(CO)4] (12) and [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))CH}-κ2-P,N}W(CO)4] (13). The reactions of 5 with [M(COD)Cl2] (M = Pd and Pt) yielded κ2-P,P chelate complexes 14 and 15, respectively, whereas the treatment of 6 with [Pd(COD)Cl2] at ambient temperature resulted in the formation of a rare fused six-membered PCP pincer complex [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))C}-κ3-P,C,P}PdCl] (16). Similar reactions of 6 with [NiCl2(DME)] and [Pt(COD)Cl2] in the presence of LiHMDS yielded [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))C}-κ3-P,C,P}NiCl] (17) and [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))C}-κ3-P,C,P}PtCl] (18), respectively. The reaction between 6 and [M(COD)Cl]2 (M = Rh and Ir) produced cationic complexes [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))CH}-κ2-P,N}Rh(C8H12)]Cl (19) and [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))CH}-κ2-P,N}Ir(C8H12)]Cl (20), respectively, whereas the reaction with [Rh(acac)(CO)2] resulted in a pincer complex [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))C}-κ3-P,C,P}Rh(CO)] (21). The structures of most of the compounds have been determined by single crystal X-ray analyses. The fused six-membered PCP palladium pincer complex 16 is found to be an excellent catalyst for the Mizoroki-Heck coupling reaction.

Catechol and 1,2,4,5-tetrahydroxybenzene functionalized cyclodiphosphazane ligands: synthesis, structural studies, and transition metal complexes.

Syntheses of two novel cyclodiphosphazane derivatives appended on catechol and 1,2,4,5-tetrahydroxy benzene, [{(µ-N(tBu)P)2(C6H4O2)}] (1) and [{((µ-N(tBu)P)2)2(µ-C6H2O4)}] (2), are described. Reactions of 1 with copper(i) halides led to the isolation of one-dimensional (1-D) and two-dimensional (2-D) coordination polymers, depending on the reaction conditions, metal-to-ligand ratio and CuX (X = Cl, Br or I) employed. The 1 : 1 reaction between 1 and CuCl yielded a 1-D coordination polymer [{(µ-N(tBu)P)2(C6H4O2)}{Cu(µ2-Cl)(NCCH3)}2]n (3) containing [Cu(µ2-Cl)]2 rhombus units. Similar reactions of 1 with CuBr and CuI produced rare 1-D coordination polymers [{(µ-N(tBu)P)2(C6H4O2)}{CuX(NCCH3)}]n (4, X = Br; 5, X = I) with discrete copper atoms linked by bridging cyclodiphosphazane ligands. However, the reactions of 1 with CuX (X = Cl, Br or I) in 1 : 2 molar ratios afforded 2-D coordination polymers [{(µ-N(tBu)P)2(C6H4O2)}2{Cu4(µ3-X)4}]n (6, X = Cl; 7, X = Br and 8, X = I) containing cuboids [Cu4(µ3-X)4] with 1 linking such units. Treatment of 1 with [RuCl2(η6-p-cymene)]2, [Rh(COD)Cl]2 and [Pd(η3-C3H5)Cl]2 in 1 : 1 molar ratios produced dinuclear complexes [{(µ-N(tBu)P)2(C6H4O2)}{RuCl2(η6-p-cymene)}2] (9), [{(µ-N(tBu)P)2(C6H4O2)}{RhCl(COD)}2] (10) and [{(µ-N(tBu)P)2(C6H4O2)}{PdCl(η3-C3H5)}2] (11), respectively. The reaction between 1 and [AuCl(SMe2)] in a 1 : 2 ratio yielded a dinuclear complex [{(µ-N(tBu)P)2(C6H4O2)}{AuCl}2] (12). The reactions of 2 with [RuCl2(η6-p-cymene)]2, [Rh(COD)Cl]2 and [Pd(η3-C3H5)Cl]2 in 1 : 2 molar ratios afforded tetranuclear complexes [{((µ-N(tBu)P)2)2(µ-C6H2O4)}{RuCl2(η6-p-cymene)}4] (13), [{((µ-N(tBu)P)2)2(µ-C6H2O4)}{RhCl(COD)}4] (14) and [{((µ-N(tBu)P)2)2(µ-C6H2O4)}{PdCl(η3-C3H5)}4] (15), respectively. The reaction of 2 with [AuCl(SMe2)] also afforded a tetranuclear complex [{((µ-N(tBu)P)2)2(µ-C6H2O4)}{AuCl}4] (16). In all these complexes, ligands preferred a bridged bidentate mode of coordination. Compounds 3-8 are the rare examples of 1-D and 2-D copper(i) coordination polymers containing cyclodiphosphazane ligands. The crystal structures of 2-8, and 15 were established by X-ray diffraction studies.