Margarita Crespo

Cyclometallated platinum complexes with thienyl imines. X-ray crystal structure of [PtMe{3-(PhCH2NCH)C4H2S}PPh3]

Abstract The reaction of [Pt 2 Me 4 (μ-SMe 2 ) 2 ] with ligands 3-(Me 2 NCH 2 CH 2 NCH)C 4 H 3 S ( 2a ) and 3-(PhCH 2 NCH)C 4 H 3 S ( 2b ) produced cyclometallation at the α-position of the thiophene ring to give the platinum(II) complexes [PtMe{3-(Me 2 NCH 2 CH 2 NCH)C 4 H 2 S}] ( 4a ) and [PtMe{3-(PhCH 2 NCH)C 4 H 2 S}SMe 2 ] ( 4b ), containing [C,N,N′] or [C,N] ligands, respectively. The reaction of these compounds with triphenylphosphine produced [PtMe{3-(Me 2 NCH 2 CH 2 NCH)C 4 H 2 S}PPh 3 ] ( 5a ) and [PtMe{3-(PhCH 2 NCH)C 4 H 2 S}PPh 3 ] ( 5b ). Compound 5b was structurally characterized. Attempts to achieve the cyclometallation of the ligands 2-(Me 2 NCH 2 CH 2 NCH)C 4 H 3 S ( 2c ) and 2-(PhCH 2 NCH)C 4 H 3 S ( 2d ) were unsuccessful and only compounds [PtMe 2 {2-(Me 2 NCH 2 CH 2 NCH)C 4 H 3 S}] ( 3c ) and [PtMe 2 {2-(PhCH 2 NCH)C 4 H 3 S}SMe 2 ] ( 3d ), in which the imine behaves as a [N,N′] or [N]-donor ligand, respectively, could be obtained. The electrochemical properties of the compounds based on cyclic voltammetry or square-wave voltammetry were studied at various temperatures. Reversible one-electron reductions, assigned to ligand-centered processes, were observed at room temperature for 5b and at lower temperatures for 4a , 4b and 5a . The reversibility varies with the ligand trans to the thienyl moiety. The one-electron oxidations always occurred in an irreversible manner and were assigned to oxidation at the platinum center. Oxidative addition of methyl iodide to 4a yielded [PtMe 2 I{3-(Me 2 NCH 2 CH 2 NCH)C 4 H 2 S}] ( 6a ), while the reactions of methyl iodide with 4b and 5b each gave mixtures of isomers, arising from oxidative addition with trans stereochemistry followed by isomerization of the resulting platinum(IV) compounds. The reaction of methyl iodide with compound 5a yielded a complex mixture of compounds.

Intramolecular activation of a C–F bond at platinum(II) in the presence of weaker C–X bonds (X = H, Cl and Br)

The reaction of [{PtMe2(µ-SMe2)}2] with the bifunctional imines (C6F5)CHNCH2(2-XC6H4)(X = H, Cl and Br) leads to selective activation of the carbon–fluorine bond even in the presence of the weaker carbon–hydrogen, –chlorine and –bromine bonds.

Reactions of [C,N,N′]-cyclometallated platinum compounds with phosphines: transphobia and effect of the chloro substituents: Crystal structure of [PtCl(3,5-C6H2Cl2CHNCH2CH2NMe2)(PPh3)2]

Abstract The reaction of [C,N,N′]-cyclometallated platinum compounds [PtX(C6H4−nClnCHNCH2CH2NMe2)] (1a–1g) with triphenylphosphine gave either [C,N]-cyclometallated compounds [PtX(C6H4−nClnCHNCH2CH2NMe2)PPh3] (2), in which PPh3 is trans to the imine nitrogen, or compounds [PtX(C6H4−nClnCHNCH2CH2NMe2)(PPh3)2] (4), with cleavage of the metallacycle. The stereochemistry of compounds 2 is the expected one according to the transphobia effect, while formation of compounds 4 takes place only when there is a chlorine atom adjacent to the metallated carbon. An ionic compound 3 has also been obtained using the chelate diphosphine 1,2-bis(diphenylphosphino)ethane. All compounds have been fully characterised including a structure determination for [PtCl(3,5-C6H2Cl2CHNCH2CH2NMe2)(PPh3)2] (4f).

Cyclometallation on platinum(II) complexes; the role of the solvent and added base donor capability on the reaction mechanisms

The reaction of PhCHNCH2CH2NMe2 with [PtCl2S2] (S = SMe2 or dmso) produces [PtCl2(PhCHNCH2CH2NMe2)] (1) in which the imine acts as a bidentate [N,N′] ligand. The cyclometallated [C,N,N′] platinum(II) complex [PtCl(C6H4CHNCH2CH2NMe2)] (2) has been obtained by refluxing a methanol solution of complex 1 in the presence of base; both complexes 1 and 2 have been characterized crystallographically. The cyclometallation process has been studied kinetically at variable temperature and pressure as a function of the base added in methanol and ethanol solutions. In all cases, the actual C–H bond activation is preceded by the Z to E isomerization of the imine; detection of this species by proton NMR has also been achieved. The kinetic, thermal and baric activation parameters associated with the two processes are indicative of a different reaction mechanism operating for the reactions when the “external” base added (NaCH3CO2) can, in fact, react with the starting material to form a new acetato complex which allows for the reactions to be intramolecular.

EFFECTS OF CHLORINE SUBSTITUENTS UPON THE FORMATION, REACTIVITY AND ELECTROCHEMICAL PROPERTIES OF PLATINUM(II) AND PLATINUM(IV) METALLACYCLES

The reactions of [Pt 2 Me 4 ( μ -SMe 2 ) 2 ] ( 1 ) with chlorinated ligands Me 2 NCH 2 CH 2 NCHAr (Ar=C 6 Cl 5 ( 2a ); 2,3,6-C 6 H 2 Cl 3 ( 2b ); 2,3,5-C 6 H 2 Cl 3 ( 2c ); 2,4-C 6 H 3 Cl 2 ( 2d ); 3,5-C 6 H 3 Cl 2 ( 2e ) and 3-C 6 H 4 Cl ( 2f )) yield either cyclometallated [C,N,N′] platinum(IV) complexes [PtMe 2 Cl(Me 2 NCH 2 CH 2 NCHR–C, N , N ′)], arising from C–Cl bond activation, or cyclometallated [C,N,N′] platinum(II) complexes [PtMe(Me 2 NCH 2 CH 2 NCHR– C , N , N ′)], arising from C–H bond activation, followed by methane elimination. These processes occur at room temperature except for the formation of compound [PtMe{Me 2 NCH 2 CH 2 NCH(3,5-C 6 H 2 Cl 2 )}] ( 4e ) which is produced in refluxing toluene, since at room temperature cyclometallation of ligand 2e is not achieved. Compound [PtMe 2 {Me 2 NCH 2 CH 2 NCH(3,5-C 6 H 3 Cl 2 )– N , N ′)}] ( 3e ), arising from coordination of the ligand to the platinum center, is obtained at room temperature. The reactions of 1 with ligands PhCH 2 NCHAr (Ar=2,3,6-C 6 H 2 Cl 3 ( 2g ) and 2,3,5-C 6 H 2 Cl 3 ( 2h )) produce cyclometallated [C,N] platinum(IV) complexes. The reactivities of the platinum complexes towards phosphines and methyl iodide have been studied. All complexes have been characterized by NMR spectroscopy and the X-ray crystal structure of [PtMe 2 Cl{Me 2 NCH 2 CH 2 NCH(3,5-C 6 H 2 Cl 2 )– C , N , N ′}] ( 4c ) has been determined. The electrochemical properties of the compounds based on cyclic voltammetry have also been studied. While the first reduction step is nearly reversible for cyclometallated platinum(II) compounds, coordination complex 3e and cyclometallated platinum(IV) compounds exhibit an irreversible reduction wave. In all cases oxidation occurs in an irreversible manner. The processes involved and the influence of the chlorine substituents are discussed.

CH and CCl bond activation in the formation of cyclometallated platinum(II) and platinum(IV) compounds with chlorinated N-benzylidenebenzylamines

Abstract Platinum substrate [Pt2Me4(μ-SMe2)2] (1) reacts with chlorinated imines 3,5-Cl2C6H3CHNCH2C6H5 (2a) and 3-ClC6H4CHNCH2C6H5 (2b) to yield cyclometallated platinum(II) compounds [PtMe(3,5-Cl2C6H2CHNCH2C6H5)(SMe2)] (4a) and [PtMe(3-ClC6H3CHz.dbnd;NCH2C6H5)(SMe2)] (4b), arising from CH bond activation followed by loss of methane. A react intermediate [PtMe2(3,5-Cl2C6H3CHNCH2C6H5)(SMe2)] (3a) was detected by 1H NMR. The reaction of [Pt2Me4(μ-SMe2)2] (1) with chlorinated imine 2,4,-Cl2C6H3CHNCH2C6H5 (2c) produces a mixture of cyclometallated platinum(II) compound [PtMe(2,4- Cl2C6H2CHNCH2C6H5)(SMe2)] (4c) and cyclometallated platinum(IV) compound [PtMe2Cl(4-ClC6H3CHNCH2C6H5)(SME2)] (4c′) arising respectively from aryl CH and aryl CCl bond activation. The reaction of complex 4a with triphenylphosphine produces metallacycle cleavage and [PtMe(3,5-Cl2C6H2CHNCH2C6H5)PPh3)2] (5a) is formed with the imine acting as a [C−] unidentate ligand. 5a crystallizes in the monoclinic space group P21/n with a = 10.899(5) A , b = 22.953(5) A and c = 17.588(9) A , β =95.14(5)° and Z = 4. Compounds 4b, 4c and 4c′ react with PPh3 to give cyclometallated compounds [PtMe(3-ClC6H3CHNCH2 C6H5)(PPh3)] (5b), [PtMe(2,4-Cl2C6H2CHNCH2C6H5)(PPh3)] (5c), and [PtMe2Cl(4-ClC6H3CHNCH2C6H5)(PPh3)](5c′) respectively. The stereo-electronic effect of chlorine substituents, as well as the NMR parameters, are discussed in relation to the observed reactivity of these compounds.

Oxidative addition of alkyl halides to chiral cyclometallated platinum(II) complexes with thienyl imines. X-ray crystal structure of [PtMe{3-((S)-PhCHMeNCH)C4H2S}SMe2]

Abstract The reaction of [Pt 2 Me 4 (μ-SMe 2 ) 2 ] with ligand 3-(( S )-PhCHMeNCH)C 4 H 3 S ( 1 ) produced the chiral cyclometallated compound [PtMe{3-(( S )-PhCHMeNCH)C 4 H 2 S}SMe 2 ] ( 2 ) which was characterized structurally. The reactions of 2 with phosphines gave compounds [PtMe{3-(( S )-PhCHMeNCH)C 4 H 2 S}L] (L=PPh 3 ( 3 ), P(2-MeC 6 H 4 ) 3 ( 4 ), Ph 2 PCH 2 CH 2 PPh 2 ( 5 )). The oxidative addition of methyl iodide to compounds 2 and 3 gave two diastereoisomers each of compounds [PtMe 2 I{3-(( S )-PhCHMeNCH)C 4 H 2 S}L] (L=SMe 2 ( 6a / 6a′ ), PPh 3 ( 7a / 7a′ )) in a ratio 2.1:1 and 2.4:1, respectively. Subsequent isomerization gave, in each case, a new pair of diastereoisomers. Compounds 4 and 5 failed to react with methyl iodide, while platinum(II) compounds [PtX{3-(( S )-PhCHMeNCH)C 4 H 2 S}PPh 3 ] (X=I ( 8 ), Br ( 9 )) were obtained in the reactions of 3 with ethyl iodide or benzylbromide.

Regioselective activation of CH bonds of naphthyl imines at platinum(II). Crystal structures of [PtMe{1-(2′-ClC6H4CH2NCH)C10H6}PPh3] and [PtMe{2-(2′-ClC6H4CH2NCH)C10H6}PPh3]

Abstract The reaction of [Pt2Me4(μ-SMe2)2] with ligands 1-(Me2NCH2CH2NCH)C10H7 (2a) and 2-(Me2NCH2CH2NCH)C10H7 (2b) carried out in acetone at room temperature produced compounds [PtMe2{1-(Me2NCH2CH2NCH)C10H7}] (3a) and [PtMe2{1-(Me2NCH2CH2NCH)C10H7}] (3b), respectively, in which the imines act as bidentate [N,N′] ligands. Cyclometallated [C,N,N′] compounds [PtMe{1-(Me2NCH2CH2NCH)C10H6}] (4a) and [PtMe{2-(Me2NCH2CH2NCH)C10H6}] (4b) were obtained by refluxing toluene solutions of compounds 3a or 3b. Reaction of [Pt2Me4(μ-SMe2)2] with ligands 1-(2′-ClC6H4CH2NCH)C10H7 (2c) and 2-(2′-ClC6H4CH2NCH)C10H7 (2d) produced straightforward metallation to yield [PtMe{1-(2′-ClC6H4CH2NCH)C10H6}SMe2] (5c) and [PtMe{2-(2′-ClC6H4CH2NCH)C10H6}SMe2] (5d) containing a [C,N] ligand. Triphenylphosphine derivatives [PtMe{1-(2′-ClC6H4CH2NCH)C10H6}PPh3] (6c) and [PtMe{2-(2′-ClC6H4CH2NCH)C10H6}PPh3] (6d) were also prepared. All compounds were characterised by NMR spectroscopies and 6c and 6d were also characterised crystallographically. For both [C,N,N′] and [C,N] systems, the metallation took place regioselectively at β-positions of the naphthyl group.

Stereoselective oxidative addition of methyl iodide to chiral cyclometallated platinum(II) compounds derived from (R)-(+)-1-(1-naphthylethylamine). Crystal structure of [PtMe{3-(R)-(C10H7)CHMeNCHC4H2S}PPh3]

Abstract The reaction of 3-(R)-(C10H7)CHMeNCHC4H3S (2a) with [Pt2Me4(μ-SMe2)2] in acetone gave the new chiral cyclometallated platinum(II) compound [PtMe{3-(R)-(C10H7)CHMeNCHC4H2S}SMe2] (3a). Addition of PPh3 produced compound [PtMe{3-(R)-(C10H7)CHMeNCHC4H2S}PPh3] (4a) which was characterized by X-ray diffraction methods. While oxidative addition of methyl iodide to 3a gave two pairs of diastereomers, the analogous reaction for 4a produced only one diastereomer of the platinum(IV) compound [PtMe2I{3-(R)-(C10H7)CHMeNCHC4H2S}PPh3] (7a). Subsequent isomerization of the resulting platinum(IV) compound gave a new pair of diastereomers in relative amounts 90 and 10%. Analogous proportions of final diastereomers were obtained for the oxidative addition of methyl iodide to the new chiral compounds [PtMe{3-(R)-(C10H7)CHMeNCHAr}PPh3] (Ar=C6H4 (4b), 2-FC6H3 (4c), 2-CF3C6H3 (4d)). The reaction of [Pt2Me4(μ-SMe2)2] with imines (R)-(C10H7)CHMeNCH(2-BrC6H4) (2e) and (R)-(C10H7)CHMeNCH(2,6-Cl2C6H3) (2f) produced intramolecular oxidative addition to yield platinum(IV) compounds with some degree of stereoselectivity.

Platinum-mediated aryl–aryl bond formation and sp3 C–H bond activation

A novel process is described in which intramolecular oxidative addition is followed by aryl-aryl bond formation and sp(3) C-H bond activation leading to a six-membered platinacycle.