Sergio Stoccoro

Reaction of platinum(II) derivatives with bis(pyrazolyl)propane. Cleavage of a C(sp3)-N bond in a bis(pyrazolyl)alkane promoted by platinum(II) derivatives. Crystal structure of cis-Pt(pzH)2CL2 (pzH = pyrazole)

The reactions of bis(pyrazolyl)propane (CH3)2C(pz)2, (pzH = pyrazole), with PtCl2, (RCN)2PtCl2 and K2[PtCl4 have been investigated, and the results compared with those described previously for the corresponding palladium(II) derivatives. In contrast with the behaviour of the palladium analogues, the platinum derivatives promote the rupture of the ligand: simple adducts of pyrazole, cis- or trans-Pt(pzH)2Cl2, or species containing the ligand [HNC(R)pz], formally arising from the insertion of a nitrile into the NH bond of pyrazole, are obtained. For comparison, the reaction of the platinum derivatives with pyrazole itself has been investigated under various conditions. The crystal structure of cis-Pt(pzH)2Cl2 has been determined by X-ray diffraction: monoclinic, space group C2/c, a 9.180(1), b 15.084(1), c 15.1445(9) A, β 101.536(7)°, Z - 8, R = 0.039, Rw = 0.040 for 2125 observed reflections.

Synthesis and characterization of gold(III) adducts and cyclometallated derivatives with 6-benzyl- and 6-alkyl-2,2′-bipyridines

The reaction of a series of 6-substituted-2,2′-bipyridines HL (N2C10H7R, R = CH2Ph, CHMePh, CMe2Ph, CH2Me, CMe3 or CH2CMe3) with HAuCl4 or Na[AuCl4] has been investigated. Under different experimental conditions, salts [H2L][AuCl4], adducts [Au(HL)Cl3] or cyclometallated derivatives [Au(L)Cl][X](X = AuCl4, BF4 or PF6) have been isolated. The cyclometallated species arise from direct activation of a C–H bond either of a phenyl or a methyl substituent. The structures of an adduct [Au{N2C10H7(CHMePh)-6}Cl3] and two metallated species [Au{N2C10H7(CMe2C6H4)-6}Cl][AuCl4] and [Au{N2C10H7(CMe2CH2)-6}Cl][BF4]·0.5H2O have been determined by X-ray diffraction. In the adduct the gold atom is bonded to the nitrogen atom of the unsubstituted pyridine ring: a long-range interaction with the other nitrogen atom is observed, Au ⋯ N 2.758(4)A. In the two cyclometallated species the bipyridines act as tridentate N,N,C anions, giving a [5,6] and a [5,5]-fused ring system, respectively. In [Au{N2C10H7(CMe2C6H4)-6}Cl]+ the hexaatomic N,C ring adopts a boat-like conformation: the structure reveals a rather short interaction between one hydrogen of the Me group in axial position and the gold atom, Au ⋯ H 2.62 A. The pentaatomic N,C ring in [Au{N2C10H7(CMe2CH2)-6}Cl]+ is not planar: the co-ordination around the gold atom is essentially square planar. The new cyclometallated complexes [Au(N,N,C)Cl]+ are compared with those derived from similarly substituted pyridines described previously.

Palladium(II) and platinum(II)-C( 3 )-substituted 2,2′-bipyridines

Reaction of Pd(OAc)2 with HL1 and HL2 (HL1=6-iso-propyl-2,2′-bipyridine; HL2=6-neo-pentyl-2,2′-bipyridine), followed by treatment with LiCl or KI, gives [PdCl(L1)]2, (1), [PdCl(L2)]2 (2), and [PdI(L2)]2 (3), respectively. The chloride bridge in complexes1 and2 is split by PPh3 to give the mononuclear species PdCl(L1)(PPh3) (4) and PdCl(L2)(PPh3) (5). Spectroscopic data provide evidence for coordination of the deprotonated ligands through a nitrogen and the C(3) atom of the 6-substituted pyridine. An analogous platinum complex PtCl(L3)(SMe2) (6) (HL3=6-tert-butyl-2,2′-bipyridine) was obtained from trans-PtClMe(SMe2)2 and HL3. The crystal structures of compounds1 and6 have been solved by X-ray diffraction analysis.

Metallation of unactivated methyl groups: platinum(II) derivatives with 6-alkyl-2,2′-bipyridines

The reaction of K 2 [PtCl 4 ] with three 6-alkyl-2,2′-bipyridines HL, (N 2 C 10 H 7 R; R = CH 2 Me, HL et ; CHMe 2 , HL ip ; CH 2 CMe 3 , HL np ) affords five- and six-membered cyclometallated complexes [Pt(L)Cl] where L is a terdentate N , N , C anionic ligand which originates from HL through direct activation of a C(sp 3 )−H bond. In the case of HL ip , metallation generates a stereogenic carbon atom β to the metal. Complex 5, [Pt(L np )Cl], having an uncommon six-membered ring containing a Pt−C(sp 3 ) bond, was studied in depth in solution, by means of 1- and 2- dimensional NMR spectroscopy, and in the solid state by X-ray diffraction. Differences are observed in the behaviour of these ligands: thus with HLet an adduct, [Pt(HL et )Cl 2 ], was also isolated and its structure was determined by X-ray diffraction. In the metallated species, the fourth ligand, Cl, can easily be substituted by neutral or anionic ligands (CO, PPh 3 , CN − ). The metallated species react with potentially bidentate ligands L′−L′′ [Ph 2 PCH 2 PPh 2 (dppm), Ph 2 P(CH 2 ) 2 PPh 2 (dppe), Ph 2 P(CH 2 ) 2 AsPh 2 (dppae)] to give, with different Pt:L ratios, mononuclear [Pt(L)(L′−L′′)] + or dinuclear [(L)Pt(μ−L′−L′′)Pt(L)] ++ cationic species. In the second case an uncommon unsupported L′−L′′ bridge is present. The cyclometallated species are stable in air and moisture, and the N , N , C system is rather robust.

Cyclometallated derivatives of platinum(II) derived from 6-(tert-butyl)-2,2′-bipyridine (HL). Crystal and molecular structure of [Pt(L)CI]

The reaction of K2[PtCI4] with 6-(tert-butyl)-2,2′-bipyridine (HL) gave [Pt(L)CI]1a a cyclometallated species resulting from direct activation of a methyl C–H bond. The structure has been determined by X-ray diffraction. The crystals contain two independent molecules: average values for the principal parameters are Pt–CI 2.300, Pt–C 2.003, Pt–N (trans to C) 2.114 and Pt–N (trans to CI) 1.948 A. The chlorine atom in 1a can easily be displaced by neutral ligands (L′); in the presence of NaBF4 the cationic species [Pt(L)(L′)][BF4](L′= PPh32, CO 3 or 3,5-dimethylpyridine 4) were isolated in good yields. With potentially bidentate neutral ligands, L″–L″[Ph2P(CH2)2PPh2(dppe), Ph2P(CH2)2AsPh2(dadpe) or Ph2PCCPPh2(dppa)], [LPt(µ–L″–L″)PtL]2+(L″–L″= dppe 5, dadpe 6 or dppa 7) or [PtL(L″–L″)]+ species (L″–L″= dppe 8 or dadpe 9) can be obtained by adequate choice of the L″–L″ : Pt molar ratio (1 : 2 or 1 : 1, respectively). The new complexes 1–9 were characterized in solution by 1H, 13C-{1H} NMR spectra.

Reactivity of 6-(2-tolyl)- and 6-(2,6-xylyl)-2,2′-bipyridines with palladium(II) derivatives. Selective C(sp3)H vs. C(sp2)H activation

Two new 6-substituted 2,2′-bipyridines, L, 6-(2-tolyl)bipy, L1, and 6-(2,6-xylyl)bipy, L2, have been synthesized. Their reactions with Na2[PdCl4] or {Pd(OAc)2} afford either 1:1 adducts [Pd(L)X2] (X=Cl, OAc) or five-membered cyclometallated derivatives [Pd(L1-H)X] arising from C(sp2)H activation. From the chloro-alkyl intermediates [Pd(L)(Me)Cl], in the presence of Na[BAr′4] (Ar′=3,5-(CF3)2C6H3), cationic species [Pd(L)(Me)(S)]+ (L=L1, L2; S=CH3CN) can be obtained. At variance, in less coordinating solvents, e.g. dichloromethane, unexpected activation of a C(sp3)H bond occurs with loss of methane, to afford 6-membered cyclometallated derivatives. The latter species were isolated as [Pd(L-H)(PPh3)][BAr′4].

Cyclometallated derivatives of palladium(II) with 1,4-benzodiazepin-2-ones. Crystal structure of (L-H)Pd(PPh3)Cl·CHCl3 (L = Prazepam: 7-chloro-1-cyclopropylmethyl-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one). Synthesis of isoindolo[2,1-d][1,4]benzodiazepine derivatives by reaction of [(L-H)PdCl]2 species with carbon monoxide

Abstract The dimeric cyclometallated derivatives of palladium(II) [( L -H)PdCl] 2 , 3 ( L = 1 , Diazepam: 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2 H -1,4-benzodiazepin-2-one) and 4 ( L = 2 , Prazepam: 7-chloro-1-cyclopropylmethyl-1,3-dihydro-5-phenyl-2 H -1,4-benzodiazepin-2-one) react with triphenylphosphine to give the complexes ( L -H)Pd(PPh 3 )Cl, 5 ( L = Diazepam) and 6 ( L = Prazepam). The crystal structure of 6 was determined by X-ray crystallography. The palladium atom is in a square planar arrangement. The deprotonated ligand is bound to the metal through the 4-nitrogen and the ortho -carbon atom of the 5-phenyl substituent. The phosphorous and the chlorine atoms are trans to the nitrogen and the carbon atoms, respectively: PdN = 2.085(2), PdP=2.263(1), PdCl = 2.377(1), PdC = 2.009(3) A. The reaction of the dimeric derivatives [( L -H)PdCl] 2 with carbon monoxide was investigated. Under mild conditions (1 atm of CO, room temperature) the unstable ( L -H)Pd(CO)Cl derivatives. 7 ( L = Diazepam) and 8 ( L = Prazepam) are formed, but at high pressure and temperature (60–100 atm of CO, 45–50°C), extrusion of palladium occurs and tetracyclic derivatives having an isoindolo ring condensed on the 1,4-benzodiazepin-2-one system, 9–12 , are obtained.

Gold(III) six-membered N boolean AND C boolean AND N pincer complexes: synthesis, structure, reactivity and theoretical calculations

The first six-membered gold(III) N^C^N pincer complex was obtained in good yield, under very mild conditions, by transmetalation of [Hg(κC-N^C^N)Cl] (N^CH^N = 1,3-bis(pyridin-2-ylmethyl)benzene, HL(1)) with Na[AuCl(4)]. The X-ray crystal structure of [Au(N^C^N)Cl][PF(6)] showed that the fused six-membered metallacycles each exist in a strongly puckered boat conformation. As shown by the (1)H NMR spectra in various solvents, the same structure is also retained in solution: no inversion of the six-membered metallacycles is observed in DMSO up to 95 °C. This correlates well with a reaction barrier of 17.5 kcal/mole, as determined by quantum chemical calculations. The reactivity of the present pincer complex is compared to that of the analogous 1,3-bis(2-pyridyl)benzene, HL(2), derivative, which has five-membered fused metallacycles. Sharp differences are found in the reactions with phosphines, such as PPh(3) and dppe (1,2-bis-diphenylphosphino-ethane), and with silver salts. Theoretical calculations were carried out on the two pincer complexes in order to try to understand these differences, and we found that the gold-chlorine bond is significantly stronger in the case of the complex containing five-membered metallacyclic rings.

Mono and dinuclear gold(I) complexes with neutral and deprotonated 1,4-benzodiazepin-2-ones. Crystal and molecular structure of (L-H)Au(PPh3)·Et2O, where L = 1,3-dihydro-7-nitro-5-phenyl-2H-1,4-benzodiazepin-2-one, nitrazepam

Abstract The preparation of a series of neutral (L)AuCL (1a–3a) and cationic [(L)Au(PPh3)] [BF4] (1b–5b) gold(I) complexes is described (L = DIAZEPAM, 1; PRAZEPAM, 2; NITRAZEPAM, 3; LORAZEPAM, 4; NIMETAZEPAM, 5). In the presence of alkali, (PPh3)AuCl reacts with 1-unsubstituted 1,4-benzodiazepin-2-ones such as NITRAZEPAM (3) and LORAZEPAM (4) to give neutral gold(I) species (L-H)Au(PPh3) (3c and 4c). The benzodiazepine anion is bonded to Au via the N(1) atom, as shown, in the case of 3c, by X-ray analysis: (L-H)Au(PPh3)·Et2O, C33H25AuN3O3P· C4H10O, monoclinic, space group P21/c, a= 12.717(9), b=19.270(7), c=14.696(3) A, β= 107.85(3)°, Z= 4. AuP = 2.238(1), AuN = 2.071(3) A. The crystal structure was determined by standard methods and refined to R = 0.028 and Rw = 0.035 on the basis of 4456 unique reflections. p ]The complex 3c reacts with [(Ph3P)Au(S)][BF4], as obtained from (PPh3)AuCl and AgBF4 in methanol, to give the dinuclear cationic species [(Ph3P)Au{μ(L-H)}Au(PPh3)] [BF4] (3d) where the deprotonated NITRAZEPAM bridges two (Ph3P)Au groups through the N(1) and N(4) atoms. All the new derivatives were characterized by elemental analyses and spectroscopic methods (IR; 1H, 31P NMR).

Cyclometallated derivatives of platinum(II) derived from 1,4-benzodiazepin-2-ones. Crystal and molecular structure of Pt(L)(HL)Cl(HL7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one, DIAZEPAM), a molecule containing a neutral and a deprotonated 1,4-benzodiazepin-2-one

Abstract The complexes [Pt(L)Cl]2 (1), Pt(L)(HL)Cl (2), (two conformers, 2a and 2b), Pt(L)(Ph3P)Cl (3), Pt(L)(3,5-Me2t-py)Cl (4) and Pt(L)(CO)Cl (5) (HL=7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one, DIAZEPAM) have been prepared and characterized by IR, MS and 1H, 13C, 31p and two-dimensional correlation NMR spectra. Complexes 1-5 contain a deprotonated DIAZEPAM coordinated to the metal through the N(4) atom and the ortho-carbon of the 5-phenyl substituent. In complex 2, as shown by a sing]e crystal X-ray structure determination, carried out on conformer 2a, in addition to the cyclometallated system, a neutral molecule of DIAZEPAM is coordinated through the N(4) atom. The crystals of compound 2a, C32H25Cl3N4O2Pt, are monoclinic, space group P21/n with a = 13.601(3), b = 15.951(5), c = 13.837(3) A, β = 96.38(2)°, Z = 4. The structure was refined to R = 0.021 and Rw = 0.032 on the basis of 4922 unique reflections with I>3σ(I). The platinum atom is in a square planar geometry with the carbon atom trans to the chloride ligand: PtC=1.983(3), PtCl=2.402(1), PtN=2.031(3) and 2.009(3) A.