Coordination chemistry of CNH2, the simplest aminocarbyne

Formation of paramagnetic metallacyclobutadienes by reaction of diaminoacetylenes with molybdenum alkylidyne complexes

The reactions of the molybdenum alkylidyne complex [MesCMo{OCMe(CF₃)₂}₃] with the diaminoacetylenes R₂NCCNR₂ (NR₂ = 4-methylpiperidinyl, NEt₂; Mes = 2,4,6-trimethylphenyl) afforded paramagnetic metallacyclobutadiene (MCBD) complexes with diaminodicarbene ligands.

Bis(cyano) Iron(III) Porphyrinates: What Is the Ground State?

The synthesis of six new bis(cyano) iron(III) porphyrinate derivatives is reported. The anionic porphyrin complexes utilized tetraphenylporphyrin, tetramesitylporphyrin, and tetratolylporphyrin as the porphyrin ligand. The potassium salts of Kryptofix-222 and 18-C-6 were used as the cations. These complexes have been characterized by X-ray structure analysis, solid-state Mössbauer spectroscopy, and EPR spectroscopy, both in frozen CH2Cl2 solution and in the microcrystalline state. These data show that these anionic complexes can exist in either the (dxz,dyz)(4)(dxy)(1) or the (dxy)(2)(dxz,dyz)(3) electronic configuration and some can clearly readily interconvert. This is a reflection that these two states can be very close in energy. In addition to the effects of varying the porphyrin ligand, subtle effects of the cyanide ligand environment in the solid state and in solution are sufficient to shift the balance between the two electronic states.

Acylated cyanoimido-complexes trans-[Mo(NCN){NCNC(O)R}(dppe)(2)]Cl and their reactions with electrophiles: chemical, electrochemical and theoretical study

Treatment of a dichloromethane solution of trans-[Mo(NCN){NCNC(O)R}(dppe)(2)]Cl [R = Me (1a), Et (1b)] (dppe = Ph(2)PCH(2)CH(2)PPh(2)) with HBF(4), [Et(3)O][BF(4)] or EtC(O)Cl gives trans-[Mo(NCN)Cl(dppe)(2)]X [X = BF(4) (2a) or Cl (2b)] and the corresponding acylcyanamides NCN(R')C(O)Et (R' = H, Et or C(O)Et). X-ray diffraction analysis of 2a (X = BF(4)) reveals a multiple-bond coordination of the cyanoimide ligand. Compounds 1 convert to the bis(cyanoimide) trans-[Mo(NCN)(2)(dppe)(2)] complex upon reaction with an excess of NaOMe (with formation of the respective ester). In an aprotic medium and at a Pt electrode, compounds 1 (R = Me, Et or Ph) undergo a cathodically induced isomerization. Full quantitative kinetic analysis of the voltammetric behaviour is presented and allows the determination of the first-order rate constants and the equilibrium constant of the trans to cis isomerization reaction. The mechanisms of electrophilic addition (protonation) to complexes 1 and the precursor trans-[Mo(NCN)(2)(dppe)(2)], as well as the electronic structures, nature of the coordination bonds and electrochemical behaviour of these species are investigated in detail by theoretical methods which indicate that the most probable sites of the proton attack are the oxygen atom of the acyl group and the terminal nitrogen atom, respectively.

Kinetic and Thermodynamic Aspects of the Regioselective Addition of Bifunctional Hydroxylaminooxime-type HO-Nucleophiles to Pt-Complexed Nitriles

The coupling between coordinated propiononitriles in trans-[PtCln(EtCN)2] (n = 2, 4) and the 1,2-hydroxylaminooximes HON(H)CMe2C(R)=NOH (R = Ph 1, Me 2) proceeds smoothly in CHCl(3) at ca. 40-45 degrees C and gives trans-[PtCln{NH=C(Et)ON(H)CMe2C(R)=NOH}2] (n = 2, R = Ph 5, Me 6; n = 4, R = Ph 7, Me 8) in 80-85% isolated yields. The reaction is highly regioselective, and both spectroscopic (IR; FAB+-MS; 1D 1H, 13C{1H}, and 195Pt NMR; and 2D 1H,13C HMQC, 1H,13C HMBC, and 1H,15N HMQC NMR) and X-ray data for 6-8 suggest that the addition proceeds exclusively via the hydroxylamine moiety of the 1,2-hydroxylaminooxime species; the existence of an oxime group remote from the nucleophile was also confirmed. Heating of 6 in air leads to its conversion to the unusual nitrosoalkane complex [PtCl2{HON=C(Me)C(Me)2N=O}] (9), whereas in the case of 5, only the metal-free salt [H3NC(Me)2C(Ph)=NOH]2(NO3)Cl.H2O (10) was isolated. To compare the kinetic aspects and trends in the addition of both types of nucleophiles (oximes and hydroxylamines; for the latter, see our recent work: Inorg. Chem. 2005, 44, 2944) to coordinated nitriles, a kinetic study of the addition of HON=C(CH2Ph)2 to [Ph3PCH2Ph][PtCl5(EtCN)] (11) to give [Ph(3)PCH(2)Ph][PtCl(5){NH=C(Et)ON=C(CH2Ph)2}] (12) was performed. The calculated rate constant k2 of 3.9 x 10(-6) M(-1) s(-1) at -20 degrees C for the addition of the oxime indicates that the hydroxylamine is, by a factor 1.7 x 10(4), more reactive toward the addition to nitriles than the oxime. Results of the synthetic, kinetic, and theoretical (at the B3LYP level of theory) studies have demonstrated that the high regioselectivity of the reactions of the 1,2-hydroxylaminooximes with ligated nitriles is both kinetically and thermodynamically controlled.

Mixed dinitrogen-organocyanamide complexes of molybdenum(0) and their protic conversion into hydrazide and amidoazavinylidene derivatives

Organocyanamides, Ntbd1;CNR(2) (R = Me or Et), react with trans-[Mo(N(2))(2)(dppe)(2)] (1, dppe = Ph(2)PCH(2)CH(2)PPh(2)), in THF, to give the first mixed molybdenum dinitrogen-cyanamide complexes trans-[Mo(N(2))(NCNR(2))(dppe)(2)] (R = Me 2a or Et 2b) which are selectively protonated at N(2) by HBF(4) to yield the hydrazide(2-) complexes trans-[Mo(NNH(2))(NCNR(2))(dppe)(2)][BF(4)](2) (R = Me, 3a, or Et, 3b). On treatment with Ag[BF(4)], oxidation and metal fluorination occur, and the ligating cyanamide undergoes an unprecedented beta-protonation at the unsaturated C atom to form trans-[MoF(NCHNR(2))(dppe)(2)][BF(4)](2) (R = Me, 4a, or Et, 4b) compounds which present the novel amidoazavinylidene (or amidomethyleneamide) ligands. Complexes 4 are also formed from the corresponding compounds 3, with liberation of ammonia and hydrazine. The crystal structure of 2b was determined by single-crystal X-ray diffraction analysis which indicates that the N atom of the amide group has a trigonal planar geometry.

Electrochemical Behaviour of trans-[FeH(CN)(dppe)2] Adducts

Electrochemical behaviour of various metallo cyano adducts of trans-[FeH(CN)(dppe)2], viz. the dinuclear complexes [FeH(dppe)2(μ-CN)PdCl2(PPh3)], [FeH(dppe)2(μ-CN)NiCl2(PCy3)], and trinuclear [{FeH(dppe)2(μ-CN)}2(ReOCl3)], [{FeH(dppe)2(μ-CN)}2PtCl(Ph)] and [{FeX(dppe)2(μ-CN)}2WCl3(OH)] (X = Cl or OH, dppe = 1,2-diphenylphosphinoethane, PCy3 = P(C6H11)3), as well as the benzoylisocyanide mononuclear adduct trans-[FeH(CNCOPh)- (dppe)2], is reported. All of them exhibit FeII/FeIII-based oxidations (which are reversible, except for trans-[FeH(CNCOPh)(dppe)2]). The metallocyanide bridges C≡N-Re-N≡C and C≡N-W-N≡C in [{FeH(dppe)2(μ-CN)}2(ReOCl3)] and [{FeX(dppe)2(μ-CN)}2WCl3(OH)], respectively, allow electronic communication between the iron centres, with possible generation of mixed-valence FeII/FeIII complexes whose comproportionation constant could be estimated in the former case. From the values of the measured oxidation potentials, the electrochemical PL and EL ligand parameters have been estimated for the metallocyanide ligands that were shown to behave as stronger net electron donors than organoisocyanides, although weaker than cyanide itself. Ligand-centred reduction processes were also observed to lead, in the cases of complexes trans-[FeH(CNCOPh)(dppe)2] (CNCOPh-based reduction) and [FeH(dppe)2(μ-CN)PdCl2(PPh3)] (PdII-based reduction in the CNPdCl2(PPh3)- metallocyanide ligand), to the dissociation of the adduct, with regeneration of the parent cyano complex trans-[FeH(CN)(dppe)2], thus reflecting the reductive decrease of the electrophilic (or Lewis acidic) character of the benzoyl and {PdCl2(PPh3)} groups.

Activation of organonitriles toward beta-electrophilic attack. Synthesis and characterization of methyleneamide (azavinylidene) complexes of rhenium

Treatment of the nitrile complexes cis-[ReCl(NCR)(dppe)(2)] (R = aryl; dppe = Ph(2)PCH(2)CH(2)PPh(2)) with [Et(2)OH][BF(4)] or SiMe(3)CF(3)SO(3) in CH(2)Cl(2) led to the formation of the methyleneamide (alkylideneamide or azavinylidene) compounds cis-[ReCl[NC(E)C(6)H(4)X-4](dppe)(2)]Y [E = H; X = OMe (1b), Me (1c), H (1d), F (1e), or Cl (1f), Y = BF(4); E = SiMe(3), X = Me (1c'), Y = CF(3)SO(3)] and trans-[ReCl[NC(H)C(6)H(4)X-4](dppe)(2)][BF(4)] [X = NEt(2) (2a), OMe (2b), H (2d), F (2e), or Cl (2f)]. They were characterized by multinuclear NMR spectrometry and X-ray crystallography (2e) which shows that the methyleneamide ligand exhibits linear (three-electron donor) geometry and behaves as a strong pi-electron acceptor. The complex (31)P[(1)H] and (1)H [NC(H)C(6)H(4)X-4] NMR patterns for the cis isomers were analyzed as ABCD and ABCDX (X part) spin systems, respectively. Complexes 1 and 2 undergo deprotonation by base to form the trans isomers of the corresponding nitrile complexes, trans-[ReCl(NCC(6)H(4)X-4)(dppe)(2)] [X = NEt(2) (3a), OMe (3b), H (3d), F (3e), or Cl (3f)] whose spectroscopic data are also presented and which on protonation give the corresponding trans isomers of the methyleneamide complexes (2). Reactions of cis-[ReCl(NCR)(dppe)(2)] with [Et(3)O][PF(6)] resulted in their oxidation and isomerization to afford trans-[ReCl(NCC(6)H(4)X-4)(dppe)(2)][PF(6)] [X = Me (4c), H (4d), or Cl (4f)].