Zinc amidinate-catalysed cyclization reaction of carbodiimides and alkynes. An insight into the mechanism.

A synthesis of iminopyridines based on zinc has been developed. The commercially available ZnEt was employed as a precatalyst for this process. A mechanism has been proposed on the basis of Density Functional Theory (DFT) studies and stoichiometric reactions.

Coordination of azol(in)ium dithiocarboxylate ligands to Au(III): unexpected formation of a novel family of cyclometallated Au(III) complexes, DFT calculations and catalytic studies.

A series of cyclometallated gold(III) complexes 21-27 of general formula [Au(dppta)(azdtc)Cl] (dppta = ,-diisopropyl-,-diphenylphosphinothioic amide-κC,S; azdtc = azol(in)ium-2-dithiocarboxylate-κS) were prepared and characterized by spectroscopic and diffractometric techniques. Treatment of [Au(dppta)(azdtc)Cl] complexes with methanol led to their quantitative transformation into a novel family of (C^S, S^S)-cyclometallated gold(III) complexes of general formula [Au(dppta)(azmtd)] (azmdt = azol(in)ium-2-(methoxy)methanedithiol-κS,S) 28-34. All the [Au(dppta)(azdtc)Cl] complexes 21-27 catalyzed the alkylation of indoles, whereas [Au(dppta)(azmtd)] complexes 28-34 were inactive.

C≡N and N≡O Bond Cleavages of Acetonitrile and Nitrosyl Ligands at a Dimolybdenum Center to Render Ethylidyne and Acetamidinate Ligands.

Extended reduction of [MoCp(μ-Cl)(μ-PBu)(NO)] () with Na(Hg) in acetonitrile (MeCN) at room temperature resulted in an unprecedented full cleavage of the C≡N bond of a coordinated MeCN molecule to yield the vinylidene derivative Na[MoCp(μ-PBu)(μ-CCH)(NO)], which upon protonation with (NH)PF gave the ethylidyne complex [MoCp(μ-PBu)(μ-CMe)(NO)] [Mo1-Mo2 = 2.9218(2) Å] in a selective and reversible way. Controlled reduction of at 273 K yielded instead, after protonation, the 30-electron acetamidinate complex [MoCp(μ-PBu)(μ-κ:κ'-HNCMeNH)(μ-NO)]PF [Mo1-Mo2 = 2.

E-H Bond Cleavage Processes in Reactions of Heterometallic Phosphinidene-Bridged MoRe and MoMn Complexes with Hydrogen and p-Block Element Hydrides.

Reactions of complexes [MoMCp(μ-PMes*)(CO)] with H and several p-block element (E) hydrides mostly resulted in the cleavage of E-H bonds under mild conditions [M = Re () and Mn (); Mes* = 2,4,6-CHBu]. The reaction with H (ca. 4 atm) proceeded even at 295 K to give the hydrides [MoMCp(μ-H)(μ-PHMes*)(CO)].

Cycloaddition and C-S Bond Cleavage Processes in Reactions of Heterometallic Phosphinidene-Bridged MoRe and MoMn Complexes with Alkynes and Phenyl Isothiocyanate.

Reactions of [MoReCp(μ-PMes*)(CO)] with internal alkynes RC≡CR yielded the phosphapropenylidene-bridged complexes [MoReCp(μ-κ:η-PMes*CRCR)(CO)] (Mes* = 2,4,6-CHBu; R = COMe, Ph). Terminal alkynes HC≡CR gave mixtures of isomers [MoReCp(μ-κ:η-PMes*CHCR)(CO)] and [MoReCp(μ-κ:η-PMes*CRCH)(CO)], with the first isomer being major (R = COMe) or unique (R = Bu), indicating the relevance of steric repulsions during the [2 + 2] cycloaddition step between Mo=P and C≡C bonds in these reactions. Similar reactions were observed for [MoMnCp(μ-PMes*)(CO)].

Reactions of Heterometallic Phosphinidene-Bridged MoMn and MoRe Complexes with Sulfur and Selenium: From Chalcogenophosphinidene- to Trithiophosphonate-Bridged Derivatives.

Reactions of [MoReCp(μ-PR*)(CO)] with S were strongly dependent on experimental conditions (R* = 2,4,6-CHBu). When using 1 equiv of sulfur, complex [MoReCp(μ-η:κ-SPR*)(CO)] was slowly formed at 313 K, with a thiophosphinidene ligand unexpectedly bridging the dimetal center in the novel μ-κ:η coordination mode, as opposed to the μ-κ:η mode usually found in related complexes. The latter underwent fast decarbonylation at 363 K to give [MoReCp(μ-η:η-SPR*)(CO)], with a six-electron donor thiophosphinidene ligand rearranged into the rare μ-η:η coordination mode.

ZnEt as a Precatalyst for the Addition of Alcohols to Carbodiimides.

We report here the use of commercially available ZnEt as an efficient precatalyst for the addition of alcohols to carbodiimides to obtain a wide range of isoureas under mild conditions. In an initial screening using methanol and commercial carbodiimides as substrates, the bulky isourea (OMe)(NHDipp)C(NDipp) (Dipp = 2,6-PrCH) was prepared for the first time using a catalytic method, and its structure confirmed by an X-ray diffraction analysis. Then, the efficiency of the precatalyst was tested with two carbodiimides, C(NPr) and C(N-tol), toward a series of alkylic and arylic alcohols and diols, with different steric and electronic properties, including the presence of other functional groups, usually with excellent conversions, especially for the more reactive aromatic carbodiimide.

Chemistry of a Nitrosyl Ligand κ:η-Bridging a Ditungsten Center: Rearrangement and N-O Bond Cleavage Reactions.

The novel nitrosyl-bridged complex [WCp(μ-PBu)(μ-κ:η-NO)(CO)(NO)](BAr) [Ar = 3,5-CH(CF)] was prepared in a multistep procedure starting from the hydride [WCp(μ-H)(μ-PBu)(CO)] and involving the new complexes [WCp(μ-PBu)(CO)](BF), [WCp(μ-PBu)(CO)(NO)](BAr), and [W(μ-κ:η-CH)Cp(μ-PBu)(CO)(NO)] as intermediates, which follow from reactions with HBF·OEt, NO, and MeNO·2HO, respectively. The nitrosyl-bridged cation easily added chloride upon reaction with [N(PPh)]Cl, with concomitant NO rearrangement into the terminal coordination mode, to give [WClCp(μ-PBu)(CO)(NO)], and underwent N-O and W-W bond cleavages upon the addition of CNBu to give the mononuclear phosphinoimido complex [WCp(NPBu)(CNBu)](BAr). Another N-O bond cleavage was induced upon photochemical decarbonylation at 243 K, which gave the oxo- and phosphinito-bridged nitrido complex [WCp(N)(μ-O)(μ-OPBu)(NO)](BAr), likely resulting from a N-O bond cleavage step following decarbonylation.

Electronic Structure and Donor Ability of an Unsaturated Triphosphorus-Bridged Dimolybdenum Complex.

The triphosphorus complex [MoCp(μ-η:η-P)(μ-PBu)] was prepared in 83% yield by reacting the methyl complex [MoCp(μ-κ:η-CH)(μ-PBu)(μ-CO)] with P at 333 K, a process also giving small amounts of the methyldiphosphenyl complex [MoCp(μ-η:η-PMe)(μ-PBu)(CO)]. The latter could be better prepared by first reacting the anionic complex Na[MoCp(μ-PBu)(μ-CO)] with P to give the diphosphorus derivative Na[MoCp(μ-η:η-P)(μ-PBu)(CO)] and further reaction of the latter with MeI. Density functional theory calculations on the title complex revealed that its triphosphorus group can be viewed as an allylic-like P ligand acting as a six-electron donor via the external P atoms, while coordination of the internal P atom involves donation from the π orbital of the ligand and back-donation to its π* orbital, both interactions having a weakening effect on the Mo-Mo and P-P connections.

Reactivity of -Phosphinoguanidines of the Formula (HNR)(PhPNR)C(NAr) toward Main Group Metal Alkyls: Facile Ligand Rearrangement from -Phosphinoguanidinates to Phosphinimine-Amidinates.

We report the reactivity of -phosphinoguanidines of the formula (HNR)(PhPNR)C(NAr) (R = Pr and Ar = 2,6-PrCH [Dipp] for , R = Pr and Ar = 2,4,6-MeCH [Mes] for , and R = Cy and Ar = Dipp for ), prepared in high yields from the corresponding trisubstituted guanidines, toward main group metal alkyls AlMe, ZnEt, MgBu, and BuLi to obtain novel phosphinoguanidinato and phosphinimine-amidinato compounds. Reactions of - with AlMe at room temperature led to the kinetic phosphinoguanidinato products [Al{κ-'-(NR)C(NAr)(NRPPh)}Me] (-), whereas the mild heating (60-80 °C) of solutions of - give the thermodynamic phosphinimine-amidinato products [Al{κ-'-(NR)C(NAr)(PPhNR)}Me] (-) after ligand rearrangement. The reactions of equimolar amounts of - and ZnEt initially give solutions containing unstable phosphinoguanidinato compounds [Zn{κ--(NR)C(NAr)(NRPPh)}Et] (-), which rearrange upon mild heating to the phosphinimine-amidinato derivatives [Zn{κ-'-(NR)C(NAr)(PPhNR)}Et] (-).

Efficient Synthesis and Multisite Reactivity of a Phosphinidene-Bridged Mo-Re Complex. A Platform Combining Nucleophilic and Electrophilic Features.

The heterometallic complex [MoReCp(μ-PR*)(CO)] () was prepared in 60% overall yield from -[MoCp(PHR*)(CO)] via a three-step procedure involving complexes -[MoCp(PClR*)(CO)] and [MoReCp(μ-PR*)(CO)] as intermediate species (R* = 2,4,6-CHBu). The PR* ligand in displays a novel asymmetric interaction with the dimetal center, involving a double bond with one atom (Mo) and a dative single bond with the other one (Re). Compound underwent thermal isomerization involving a C-H bond cleavage to yield the hydride [MoReCp(μ-H){μ-P(CHCMe)CHBu}(CO)] and reacted with I to give [MoReCpI(μ-PR*)(CO)], which displays a symmetrical phosphinidene bridge.

P-N and N-Mo Bond Formation Processes in the Reactions of a Pyramidal Phosphinidene-Bridged Dimolybdenum Complex with Diazoalkanes and Organic Azides.

The reactivity of the complex [MoCp(μ-κ:κ,η-PCH)(CO)(η-HMes*)(PMe)] () toward different diazoalkanes and organic azides was investigated. The pyramidal phosphinidene ligand in displayed a strong nucleophilicity, enabling these reactions to proceed rapidly even below room temperature. Thus, reacted rapidly at 253 K with different diazoalkanes NCRR' (R,R' = H,H, Ph,Ph, H,COEt) to give the corresponding P:P-bridged phosphadiazadiene derivatives as major products which, however, could not be isolated.

Coordination and Dehydrogenation of Diphosphine-Borane PhPCHPPh·BH at a Heterometallic MoRe Center to Give an Agostic Boryl-Bridged Derivative.

The coordination chemistry of the title diphosphine-borane adduct at heterometallic MoRe centers was examined through its reactions with the hydride complex [MoReCp(μ-H)(μ-PCy)(CO)(NCMe)] (Cp = η-CH). The latter reacted rapidly with stoichiometric amounts of dppm·BH (dppm = PhPCHPPh) in refluxing toluene solution, with displacement of the nitrile ligand, to give [MoReCp(μ-H)(μ-PCy)(CO)(κ-dppm·BH)], with a -bound diphosphine-borane ligand arranged to the PCy group. Decarbonylation of the latter complex was accomplished rapidly upon irradiation with visible-UV light in toluene solution at 263 K, to give the agostic derivative [MoReCp(μ-H)(μ-PCy)(CO)(κ,η-dppm·BH)] as major product (Mo-Re = 3.

One-step synthesis and P-H bond cleavage reactions of the phosphanyl complex syn-[MoCp{PH(2,4,6-CHBu)}(CO)] to give heterometallic phosphinidene-bridged derivatives.

Photolysis of [Mo2Cp2(CO)6] and PH2R* (R* = 2,4,6-C6H2tBu3) yielded the title complex, which turned out to be a versatile precursor of novel heterometallic phosphinidene-bridged complexes via three different P-H bond activation processes: photolysis, deprotonation and reduction. In this way the new complexes [MoReCp(μ-PR*)(CO)n] (n = 6,7), [MoFeCp2(μ-PR*)(CO)m], (m = 3, 4) and [MoAuCp(μ-PR*)(CO)2{P(p-tol)3}] were prepared.

9-Borabicyclo[3.3.1]nonane: a metal-free catalyst for the hydroboration of carbodiimides.

The commercial 9-borabicyclo[3.3.1]nonane dimer is used as the first example of a metal-free catalyst for the monohydroboration of carbodiimides with pinacol borane.

Unusual ligand rearrangement: from N-phosphinoguanidinato to phosphinimine-amidinato compounds.

Novel N-phosphinoguanidines (HNiPr)(Ph2PNiPr)C(NAr) (Ar = 2,6-iPr2C6H3, 2,4,6-Me3C6H2) react with AlMe3 to afford phosphinimine-amidinato derivatives, via an unprecedented rearrangement of an initial N-phosphinoguanidinato intermediate. A reasonable mechanism has been proposed for this transformation, supported by DFT calculations, involving carbodiimide de-insertion followed by a [3+2] cycloaddition.

N-O Bond Activation and Cleavage Reactions of the Nitrosyl-Bridged Complexes [MCp(μ-PCy)(μ-NO)(NO)] (M = Mo, W).

The title complexes (1a,b) were prepared in two steps by first reacting the hydrides [MCp(μ-H)(μ-PCy)(CO)] with [NO](BF) in the presence of NaCO to give dinitrosyls [MCp(μ-PCy)(CO)(NO)](BF), which were then fully decarbonylated upon reaction with NaNO at 323 K. An isomer of the Mo complex having a cisoid arrangement of the terminal ligands ( cis-1a) was prepared upon irradiation of toluene solutions of 1a with visible-UV light at 288 K. The structure of these trinitrosyl complexes was investigated using X-ray diffraction and density functional theory (DFT) calculations, these revealing a genuine pyramidalization of the bridging NO that might be associated in part to an increase of charge at the N atom and anticipated a weakening of the N-O bond upon reaction with bases or reducing reagents.

Dehydrogenation, Methyl Elimination and Insertion Reactions of the Agostic Methyl-Bridged Complex [Mo Cp (μ-κ :η -CH )(μ-PtBu )(μ-CO)].

The high unsaturation of the title complex enabled it to react with a wide variety of molecules under mild conditions, whereby the agostic methyl ligand underwent unusual or unprecedented processes. Methane elimination occurred in the reactions with PPh H and SiPh H , this being followed in the latter case by Si-H bond oxidative addition to give the hydride silylene derivative [Mo Cp H(μ-PtBu )(μ-SiPh )(CO)]. Dehydrogenation, however, was the dominant process in the room temperature reaction with [Fe (CO) ], to give the unsaturated methylidyne cluster [Mo FeCp (μ -CH)(μ-PtBu )(CO) ] (Mo-Mo=2.

Reply to the 'Comment on "Hydride, gold(i) and related derivatives of the unsaturated ditungsten anion [WCp(μ-PCy)(μ-CO)]"' by M. Green, Dalton Transactions, 2018, 47, DOI: 10.1039/C8DT00044A.

The half-electron and CBC representations of the hydride-bridged complexes [M2Cp2(μ-H)(μ-PR2)(CO)2] are analyzed. It is shown that the former gives a picture in good agreement with the physicochemical properties of these species, while keeping simplicity.

Carbodiimides as catalysts for the reduction of CO with boranes.

Carbodiimides catalyse the reduction of CO2 with H-BBN or BH3·SMe2 to give either mixtures of CH2(OBBN)2 and CH3OBBN or (MeOBO)3 and B(OMe)3 under mild conditions (25-60 °C, 1 atm CO2). Stoichiometric reactions and theoretical calculations were performed to unveil the mechanism of these catalytic processes.

E-H Bond Activation and Insertion Processes in the Reactions of the Unsaturated Hydride [WCp(μ-H)(μ-PPh)(NO)].

The reactions of the title complex (1) with different p-block element (E) molecules was examined. Compound 1 reacted with BH·THF at room temperature to give the trihydride [WCp(μ-H)H(μ-PPh)(NO)], which formally results from hydrogenation of 1, a reaction that actually does not take place when neat dihydrogen is used. Clean E-H bond oxidative addition, however, took place when 1 was reacted with HSnPh, to give the related dihydride stannyl derivative [WCp(μ-H)H(μ-PPh)(NO)(SnPh)].

Phosphinidene-Bridged MoMn Derivatives of the Thiophosphinidene Complex [MoCp(μ-κ:κ,η-SPMes*)(CO)] (Mes* = 2,4,6-CHBu).

The title complex (1) reacted with [Mn(CO)] under visible-UV irradiation (toluene solution and quartz glassware) to give a mixture of the phosphinidene complex [MnMoCp(μ-κ:κ,η-PMes*)(CO)], the cluster [MnMoCp(μ-κ:κ,η-PMes*)(μ-S)(CO)], and the thiophosphinidene complex [MnMoCp(μ-κ:κ,η-SPMes*)(CO)], in yields of ca. 60, 20, and 10% respectively (Mes* = 2,4,6-CHBu). The major product follows from formal replacement of the SMoCp(CO) fragment in 1 with a Mn(CO) fragment, and displayed multiple bonding to phosphorus (Mn-P = 2.

Acetonitrile Adduct [MoReCp(μ-H)(μ-PCy)(CO)(NCMe)]: A Surrogate of an Unsaturated Heterometallic Hydride Complex.

The title compound was prepared upon irradiation of acetonitrile solutions of the readily available hexacarbonyl [MoReCp(μ-H)(μ-PCy)(CO)]. The acetonitrile ligand in this compound could be replaced easily by donor molecules or displaced upon two-electron reduction. In most cases, the substitution step was followed by additional processes such as insertion into the M-H bonds, E-H bond cleavage, H elimination, and other transformations.

Structure and dynamics of heterometallic clusters derived from addition of metal carbonyl fragments to the unsaturated hydride [WCp(μ-H)(μ-PPh)(NO)].

The title complex reacted with [Fe(CO)] to give the trinuclear derivative [FeWCp(μ-H)(μ-PPh)(CO)(NO)] (W-W = 3.044(1) Å) as a result of full insertion of the 16-electron Fe(CO) fragment into the tricentric W-H-W bond of the parent substrate. In contrast, the reactions with the THF adducts [M(CO)(THF)] (M = W, Mo) and [MnCp'(CO)(THF)] (Cp' = CHMe) yielded the μ-hydride derivatives [MWCp(μ-H)(μ-PPh)(CO)(NO)] (W-W = 3.