Isonitriles RNC Research Articles

Gallaphosphene L(Cl)GaPGaL: A novel phosphinidene transfer reagent.

Gallaphosphene L(Cl)GaPGaL 1 (L=HC[C(Me)N(Ar)]2; Ar=2,6-iPr2C6H3) reacts with N-heterocyclic carbenes RNHC (RNHC=[CMeN(R)]2C; R=Me, iPr) to RNHC-coordinated phosphinidenes RNHC→PGa(Cl)L (R=Me 2 a, iPr 2 b) and with isonitriles RNC (R=iPr, Cy) to 1,3-phosphaazaallenes L(Cl)GaP=C=N-R (R=iPr 3 a, Cy 3 b), respectively. Quantum chemical calculations reveal that 2 a/2 b possess two localized lone pair of electrons, whereas 3 a/3 b only show one localized lone pair as was reported for gallaphosphene 1. 2 b reacts with 2.5 equivalents of a borane (THF ⋅ BH3) to the NHC-stabilized phosphinidene-borane complex [iPrNHC→P(BH2)]2(BH3)3 4 with concomitant formation of LGa(H)Cl 5. 2-5 are characterized by heteronuclear (1H, 13C{1H}, 31P{1H}) NMR and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction (sc-XRD).

(η5-C5Me5)2U(=P-2,4,6-tBu3C6H2)(OPMe3) Revisited—Its Intrinsic Reactivity toward Small Organic Molecules

The Lewis base stabilized uranium phosphinidene (η5-C5Me5)2U(═P-2,4,6-tBu3C6H2)(OPMe3) (2), which was derived from (η5-C5Me5)2U(Cl)Me (1) and 2,4,6-(Me3C)3C6H2PHK in toluene in the presence of Me3PO, was originally reported in 1996, but since then its reactivity toward small organic molecules has not been extensively explored. This contribution closes this gap, and divergent reactivity patterns are established in the reaction of complex 2 toward (small) organic substrates. For example, complex 2 may release the phosphinidene moiety (2,4,6-tBu3C6H2P:) and therefore may act as a source of a (η5-C5Me5)2UII fragment in the presence of Ph2S2, Ph2Se2, bipy, ketazine (Ph2C═N)2, and conjugated alkynes RC≡CC≡CR, forming the disulfido compound (η5-C5Me5)2U(SPh)2 (5), diselenido compound (η5-C5Me5)2U(SePh)2 (6), bipy compound (η5-C5Me5)2U(bipy) (8), diiminato compound (η5-C5Me5)2U(N═CPh2)2 (9) and the metallacyclopentatrienes (η5-C5Me5)2U[η4-C4(R)2] (R = Ph (10), Me3Si (11)), respectively. Furthermore, compound 2 may also straightforwardly react with terminal alkynes and a variety of heterounsaturated (organic) molecules such as CS2, isothiocyanates, imines, diazenes, carbodiimides, nitriles, isonitriles, and organic azides. For instance, on treatment with phenylacetylene (PhC≡CH) the dialkynyl uranium complex (η5-C5Me5)2U(C2Ph)2(OPMe3) (12) is formed, whereas CS2 and PhNCS furnish the carbodithioates (η5-C5Me5)2U[SC(═P-2,4,6-tBu3C6H2)S](OPMe3) (13) and (η5-C5Me5)2U[SC(═NPh)S](OPMe3) (14), respectively. In the reaction of the secondary aldimine PhCH═NPh or the diazene PhN═NPh and 2 the uranium(IV) imido complex (η5-C5Me5)2U(═NPh)(OPMe3) (15) is isolated, which is in contrast to its reactivity with the primary ketimine 9-(C12H8)C═NH and the carbodiimides (RN═)2C, yielding the diiminato uranium(VI) complex (η5-C5Me5)2U[N═C(C12H8)]2 (16) and the four-membered uranaheterocycles (η5-C5Me5)2U[N(R)C(═P-2,4,6-tBu3C6H2)N(R)] (R = C6H11 (17), iPr (18)), respectively. Furthermore, treatment of 2 with nitriles RCN affords the imido uranium(IV) complexes (η5-C5Me5)2U[═NC(═P-2,4,6-tBu3C6H2)R](OPMe3) (R = C6H11 (19), Me3C (20)), whereas isonitriles RNC furnish the metallaaziridines (η5-C5Me5)2U[C(═P-2,4,6-tBu3C6H2)N(R)](OPMe3) (R = C6H11 (21), 2,6-Me2Ph (22)). However, in the reaction with organic azides RCN3, complex 2 yields the imido uranium(IV) complexes (η5-C5Me5)2U(═NR)(OPMe3) (R = Ph3C (23), p-tolyl (24)) as a result of 3,3-Me2-5,7-tBu2C8H5P (7) formation and N2 release. The new compounds 12–24 were characterized by various spectroscopic techniques, including single-crystal X-ray diffraction analyses. Furthermore, with complex 2 in hand a comparison between the reactivity of uranium phosphinidenes differing in the steric bulk of its cyclopentadienyl ligands and the effects of a Lewis base (OPMe3) adduct was undertaken.

Synthesis, Bonding and Reactivity of a Terminal Titanium Alkylidene Hydrazido Compound

We report a detailed study of the reactions of the Ti=NNCPh2 alkylidene hydrazide functional group in [Cp*Ti{MeC(NiPr)2}(NNCPh2)] (8) with a variety of unsaturated and saturated substrates. Compound 8 was prepared from [Cp*Ti{MeC(NiPr)2}(NtBu)] and Ph2CNNH2. DFT calculations were used to determine the nature of the bonding for the Ti=NNCPh2 moiety in 8 and in the previously reported [Cp2Ti(NNCPh2)(PMe3)]. Reaction of 8 with CO2 gave dimeric [(Cp*Ti{MeC(NiPr)2}{μ-OC(NNCPh2)O})2] and the "double-insertion" dicarboxylate species [Cp*Ti-{MeC(NiPr)2}{OC(O)N(NCPh2)C(O)O}] through an initial [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(O)O}], the congener of which could be isolated in the corresponding reaction with CS2. The reaction with isocyanates or isothiocyanates tBuNCO or ArNCE (Ar = Tol or 2,6-C6 H3 iPr2 ; E = O, S) gave either complete NNCPh2 transfer, [2+2] cycloaddition to Ti=Nα or single- or double-substrate insertion into the Ti=Nα bond. The treatment of 8 with isonitriles RNC (R = tBu or Xyl) formed σ-adducts [Cp*Ti{MeC(NiPr)2}(NNCPh2)(CNR)]. With Ar(F5)CCH (Ar(F5)=C6F5) the [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(Ar(F5))C(H)}] was formed, whereas with benzonitriles ArCN (Ar = Ph or Ar(F5)) two equivalents of substrate were coupled in a head-to-tail manner across the Ti=Nα bond to form [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(Ar)NC(Ar)N}]. Treatment of 8 with RSiH3 (R = aryl or Bu) or Ph2SiH2 gave [Cp*Ti{MeC(NiPr)2}{N(SiHRR')N(CHPh2)}] (R' = H or Ph) through net 1,3-addition of Si-H to the N-N=CPh2 linkage of 8, whereas reaction with PhSiH2X (X = Cl, Br) led to the Ti=Nα 1,2-addition products [Cp*Ti{MeC(NiPr)2}(X){N(NCPh2)SiH2Ph}].

Synthesis and Reactivity toward Isonitriles of (2-Aminoaryl)palladium(II) Complexes

Mixtures of “Pd(dba)2” (dba = dibenzylideneacetone) and 2,2‘-bipyridine (bpy; 1:2) or N,N,N‘,N‘-tetramethylethylenediamine (tmeda; 1:1) react with 2-bromo-4-nitroaniline to give [Pd{C6H3NH2-2-NO2-5}Br(N−N)] (N−N = bpy (1b), tmeda (1b‘)). Reactions of 2-iodoaniline with mixtures of “Pd(dba)2” and isonitriles RNC (R = C6H3Me2-2,6 (Xy), 2:1:2 molar ratios; R = tBu, 2.9:1:2 molar ratios) result in the formation of the complexes [Pd{κ2C,N-C(NXy)C6H4NH2-2}I(CNXy)] (2a) and trans-[Pd{C(NtBu)C6H4NH2-2}I(CNtBu)2] (3a*). The reactions of [Pd{C6H4NH2-2}I(bpy)] and 1b‘ with RNC give the complexes trans-[Pd{C(NR)C6H3NH2-2-Y-5}}X(CNR)2] (Y = H, X = I, R = Xy (3a), tBu (3a*); Y = NO2, X = Br, R = Xy (3b), tBu (3b*)). Complexes 3 react with Tl(TfO) (TfO = CF3SO3) to give decomposition products, with the exception of 3a, which gives the cyclopalladated complex cis-[Pd{κ2C,N-C(NXy)C6H4NH2-2}(CNXy)2]TfO (4a). Complex 2a or 3 reacts with Tl(TfO) in the presence of the corresponding ligand, L or L2, to give the cationic complex [Pd{C(NR)C6H3NH2-2-Y-5}(CNR)L2]TfO (L = tBuNC, Y = H (5a*), NO2 (5b*); L2 = bpy, Y = H, R = Xy (6a), tBu (6a*)). When L = PPh3, the resulting complexes trans-[Pd{C(NR)C6H3NH2-2-Y-5}(CNtBu)2(PPh3)]TfO (Y = H (7a*), NO2 (7b*)) decompose easily to the Pd(I) complex [Pd2(CNtBu)4(PPh3)2](TfO)2 (8). The reaction of 2a with Tl(TfO) affords [{Pd[κ2C,N-C(NXy)C6H4NH2](CNXy)}2(μ-I)]TfO (9a), and that with a mixture of bpy and Tl(TfO) in acetone with subsequent bubbling of CO through the solution gives [Pd(R)(CNXy)(bpy)](TfO)2 (10), where R is 2-(xylylamino)-3-xylylquinazolinium-4-yl. The crystal structures of 2a, 3a, 4a, 6a, 8, 9a·CH2Cl2, and 10·1.5CH2Cl2 have been determined by X-ray diffraction studies. Some hydrogen bond interactions (Csp3−H···Pd, N−H···π−arene, N−H···I−Pd; eight-membered rings ···O−S−O···H−N−C−C−H··· and ···I−Pd−N−H···I−Pd−N−H···) lead to interesting supramolecular structures.

Coordination Chemistry of the Heme in Cystathionine β-Synthase: Formation of Iron(II)–Isonitrile Complexes

Interaction of rat and human cystathionine-β-synthase (CBS) with various potential ligands has been studied by visible and EPR spectroscopy in order to explore the coordination chemistry of this atypical hemeprotein. Ferric CBS did not react with any classical hemeprotein ligands, such as various imidazole and pyridine derivatives, N−3 and isonitriles RNC. Ferrous CBS also failed to bind these nitrogenous ligands or nitrosoalkanes. However, it reacts with various isonitriles RNC, leading to complexes characterized by a Soret peak at 433 ± 2 nm. Binding of isonitriles to ferrous CBS is a relatively slow process; its rate markedly depends on the nature of R. It thus seems that the only exogenous ligands able to bind CBS iron are carbon-centered, very strong heme–Fe(II) ligands such as CNR, CO, and CN−, presumably after dissociation of the CBS–iron(II)–cysteinate bond. Isonitriles appear as interesting tools for further studies on the topology of CBS active site.

The First Examples of Isonitrile Insertion into a Phosphido Bridge and the Crystal and Molecular Structures of [Pt2(μ-PBut2){μ,η2-P(But2)C(NAr)}(CNAr)2] and [Pt{μ,η2-P(But2)C(NHAr)}(CNAr)]2(CF3SO3)2 (Ar = p-Tolyl)

The platinum(I) dinuclear carbonyl [Pt2(μ-PBut2)2(PBut2H)(CO)] (1) reacts with organic isonitriles RNC (R = p-tolyl, But, PhCH2), yielding the mono- and disubstituted derivatives [Pt2(μ-PBut2)2(PBut2H)(CNR)] (2, R = p-tolyl; 3, R = But; 4, R = PhCH2) and [Pt(μ-PBut2)(CNR)]2 (5, R = p-tolyl; 6, R = But; 7, R = PhCH2). Only with the aromatic isonitrile does the reaction proceed through two further well-separated steps, giving [Pt2(μ-PBut2){μ,η2-P(But2)C(NAr)}(CNAr)2] (8) and [Pt{μ,η2-P(But2)C(NAr)}(CNAr)]2 (9). These arise from the unprecedented reversible isonitrile insertion into the M−P bonds of the phosphido-bridges. When 8 or 9 are reacted with CF3SO3H, the cyclic carbenes [Pt2(μ-PBut2){μ,η2-P(But2)C(NHAr)}(CNAr)2]CF3SO3 (10) and [Pt{μ,η2-P(But2)C(NHAr)}(CNAr)]2 (CF3SO3)2 (11) are respectively formed. The crystal and molecular structures of complexes 8 and 11 were solved by X-ray diffraction.

Tri‐tert‐butylazadiboriridin: Ringerweiterung mit Isonitrilen, α‐Bromlithioalkanen und Aziden

Tri‐tert‐butylazadiboriridine: Ring Prolongation by the Action of Isonitriles, α‐Bromolithioalkanes, and AzidesIsonitriles ArNC are 1,1‐boroborated by the B‐B bond of the azadiboriridine (‐BR‐BR‐NR‐) (1; R = tBu) to form the four‐membered ring [‐BR‐C(NAr)‐BR‐NR‐] (2b; Ar = 2,6‐C6H3Me2). Corresponding rings undergo [3 + 3] cyclodimerization of the B‐C=N chain to give the tricyclic products 6a, b when isonitriles RNC with the small ligands R = Me, Et are boroborated by 1. Two molecules of tBuNC open the B‐B bond of 1; the resulting five‐membered ring 7a may add excess tBuNC to yield 7a · 2 CNtBu (8). The results strongly support a mechanistic hypothesis set up for the multistep reaction of 1 and CO. The carbene units, which are present in the α‐bromolithioalkanes [‐C(Br)Li‐CMe2‐CH2‐], LiC(Br)H2, and LiC(Br)Me2, are also 1,1‐boroborated by 1 to give the corresponding four‐membered ring 2c, or by a 2:1 reaction to afford the five‐membered ring 7b, or by a 1:1 reaction and subsequent rearrangement to yield the five‐membered ring 7c. The nitrene units, which are present in the azides PhN3 and PhCH2N3, are also boroborated by 1; the diazadiboretidines 5b, c are formed with evolution of N2. The bis(diazadiboretidinyl)borane RB(N2B2R3)2 (5d) is the corresponding product from the reaction of RB(N3)2 with 1 in the ratio 1:2. The azide Me3SiN3 reacts differently yielding the N‐boryl diazadiboretidine 5e and the iminoborane RB≡N̊. The B‐B bond length of 187.6 pm in 5e indicates a transannular bonding interaction. The products 5d, 5e, and 6a were characterized by a crystal structure analysis.

C 1-insertion reactions at cyclodimeric ( η2-acetaldehyde) zirconocene complexes

Carbonylation of dimethylzirconocene, followed by treatment with zirconocene dihydride, benzyl chloride and then methyllithium, gave the ( η 2-acetaldehyde)zirconocene dimer ( 9) as a mixture of trans- and cis-isomers isolated in a 1.5:1 ratio under kinetic control and in a 1:1.7 ratio under thermodynamic control, respectively. Complexes trans- 9/ cis- 9 were treated with carbon monoxide to give the rans- 10 / cis- 10 monoinsertion products, and with isonitriles RNC (R = CH 2SiMe 3 ( a), CMe 3 ( b)) to give the mono- and bis-insertion product trans- and cis- 11(a, b) and 12(a, b), respectively. Complex 12a was characterized by X-ray diffraction. In all cases the trans / cis stereochemical information was predominantly retained in the products, which indicates that dimetallic pathways are favoured in these insertion reactions of the metallatricyclic ( η 2-aldehyde)metallocene dimers.

Polare Iminoborane: Reaktionen des (tert‐Butylimino)(pentafluorphenyl)borans

AbstractPolar Iminoboranes: Reactions of (tert‐Butylimino)(pentafluorophenyl)boraneThe reactions of the iminoborane C6F5‐B≡N‐tBu (1) with nitriles and isonitriles are studied. Nitriles RCN give cycloadducts either of the triazadiboracyclohexane type (3a; R = iPr) or of the tetrazatriborabicyclo[4.2.0]octane type [4b‐d; R = Ph, p‐C6H4Me, p‐C6H4(CF3)] or of the (iminomethyl)borazine type (5e, f; R = Me, Et). Isonitriles RNC yield mainly adducts of RNC to a cycloaddition product of the diazadiboracyclopentane type (6a, b; R = 2,6‐C6H3Me2, tBu); the adduct of RNC to a diazadiboracyclobutane may be a side‐product (7b; R = tBu). The iminoborane Me3Si(tBu)N‐B=NtBu reacts with two molecules of (2,6‐C6H3Me2)NC to give the corresponding azaboracyclobutane 8. The iminoborane tBu‐B≡N‐C6F5 (1′), formed by gas‐phase elimination of ClSiMe3 from Cl(tBu)B = N(C6F5)SiMe3 (9), cyclodimerizes more readily than the isomeric borane 1. The cyclodimer 2′ gives 1:1‐addition reactions with tBuNC, PMe3, and MeNC, respectively; the added components fluctuate in solutions of the products 7b'‐d'. A similar fluctuation is observed with the 1:1 adduct 7c from PMe3 and the cyclodimer 2 of the iminoborane 1. The products 3a, 5e, 6a, 8 crystallize in the space groups P21/c, P21/n, Pbca, and P21/c, respectively.

Reactions of the 12-electron alkoxide-supported tungsten clusters W4(OR)12 (R = CH2-iso-Pr, cyclopentylmethyl) with isocyanides, nitriles, nitric oxide, and alkynes. Comparison with the reactivity of W2(OR)6 compounds

The reactions between W 4 (OR) 12 compounds, where R=CH 2 -i-Pr and CH 2 -c-Pen, and the isonitriles RNC, where R=t-Bu, PhCH 2 , and mesityl (2,4,6-C 6 H 2 Me 3 ), in hydrocarbon solvents at 22 o C yield the previously characterized μ 4 -carbido clusters W 4 (μ 4 -C)(OR) 14 by cleavage of the C≡N bond.

Synthesis and reactivity of palladium(I) derivatives with bis(diphenylphosphino)amine. X-ray crystal structure of Pd 2(μ-dppa) 2Cl 2·(CH 3) 2CO

ClPd(μ-dppa) 2PdCl [dppa = bis(diphenylphosphino)aminel ( 1) has been prepared by treating PdCl 2(NCPh) 2 with Pd 2(dba) 3·.CHCl 3 (dba = dibenzylideneacetone) and dppa in CH 2Cl 2. Substitution reactions allow the synthesis of the neutral BrPd(μ-dppa) 2 PdBr ( 2) and the cationic [Ph 3PPd(μ-dppa) 2PdPPh 3](BPh 4) 2 ( 4) derivatives. Complex 1 reacts with SnCl 2 yielding Cl 3SnPd(μ-dppa) 2PdSnCl 3 ( 3). The species R 2N + and SO 2 insert into the PdPd bond of 1 to give the appropriate A-frame Pd II-Pd II complexes. Extrusion of SO 2 takes place at room temperature. CO does not react with 1 in CH 2Cl 2 at room temperature. The insertion-elimination reactions of 1 with isonitriles RNC (R = p-Tol Cy) have been studied. The molecular structure of ClPd(μ-dppa) 2PdCl·(CH 3) 2CO has been established by a single crystal X-ray study. The crystals are monoclinic, space group P2 1/ c, with a = 13.540(3), b = 16.943(2), c = 21.082(15) Å, β = 105.257(42)° and Z = 4. The final R factor was 0.033 for 5091 observed reflections. The PdPd distance is 2.6378(6) Å.

Synthesis and reactivity of mixed pentafluorophenylpalladium(I)-platinum(I) derivatives molecular structure of ClPt(μ-dppm) 2 Pd(C 6F 5)

XPt(μ-dppm) 2 Pd(C 6F 5) (X  Cl (I), Br (II), C 6F 5 (III) have been prepared by treating PdX(C 6F 5)(η 1-dppm) 2 with Pt(COD) 2 or Pt(PPh 3) 4. Substitution reactions of I yield neutral (SCN) or cationic (PPh 3, py) derivatives. The species R 2N +, SO 2 or RCCR (R  COOMe) insert into the PdPt bond of I to give A-frame Pd II-Pt II complexes, but reaction with SnCl 2 gives the SnCl 3 − derivative. The reactions of X-Pt(μ-dppm) 2Pd(C 6F 5) (X  Cl (I), C 6F 5 (III)) with isonitriles RNC (R  p-Tol, Cy, t-Bu) has been studied; the nature of the products obtained depends on the starting material, the isonitrile, and the reaction conditions. The molecular structure of ClPt(μ-dppm) 2Pd(C 6F 5) has been established by a single crystal X-ray study.

Structural chemistry and reactivity of cluster bound acetylides: close relatives of the carbides?

There is a great deal of current interest in the chemistry of unsaturated molecules bound in multi-site fashion along the edges or across the faces of bior polynuclear metal compounds. A principal reason for this interest lies in the belief that the interaction of a ligand with several metal atoms may produce unusual patterns of chemical reactivity capable of synthetic exploitation. Particular attention has focussed on CO and carbide ligands in the context of Fischer-Tropsch and related processes. Our efforts have centred on a group of ligands the acetylides, related to both CO and carbides. From a chemical standpoint, cluster bound acetylides RCECoffer a number of attractive features: (i) a variety of multi-site bonding modes (e.g. sym-p2, P2fl, J3fl, is accessible in clusters (ii) as in some carbides the cx(to M) carbon atom is bare (iii) the polarity (and hence reactivity) of the unsaturated linkage can be varied by changing the electronic characteristics of the group R. Syntheses and structural systematics for the polynuclear ruthenium compounds Ru2(CO)6(ii2-2-CECR)(PPh2), Ru3(CO)8_9(1i3-fl2-CECR)(PPh2) , Ru(CO)13 (i-i2-fl2-CECR)(PPh2), Ru5(CO)13(-2-CECR)(PPh2) (R=Ph, But, Pr') and the bis (acetylides) Ru3(CO)6 (p2-CECR) (i2-2-CECR) (PPh2)2 (Ph2PCECR) and Ruk (CO) 8(p2-ii2-CECR) (p3-2-CECR) (PPh2)2(Ph2PCECR) will be described. The Carbocationic' nature of the acetylides in these molecules is shown by their reactivity towards nucleophiles (eg. C-C coupling occurs with isonitriles RNC). Reactions of cluster carbides with H2 are the subject of extensive investigation at present. The acetylides Ru3(CO)8(p3-CECR) (PPh2) and Ru5(CO)13(p-n2-CECPh)(PPh2) undergo facile reduction with H2 affording olefin or alkane and hydrido bridged clusters Ru3(CO)9(H)(PPh2) and Ru3(CO)g(H)2(PPh). The structure of Ru3(CO)g(H)(PPh2) provides a remarkable insight into P-C bound activation leading to P-C cleavage and generation of the phosphinidene Ru3(CO)9(H)2(PPh2). INTRODUCTION A major impetus for the growth of transition metal cluster chemistry, apart from the intrinsic fascination of inorganic chemists with catenated species and molecular geometry, can be traced to the belief that multi-site binding on a cluster surface may be a key to the activation and subsequent elaboration of small molecules (1,2). As a prime example, the potential of synthesis gas (CO/H2 mixtures) as a source of petrochemicals has spurred efforts to investigate the chemistry of CO activated via interactions with several metal itoms (3), and the chemical behaviour of certain proposed model intermediates in Fischer-Tropsch processes including cluster carbides,methylidyne, methylene, formyl and hydroxymethyl complexes. In the particular context of cluster carbides, there is accumulating evidence that exposed' low coordinate carbide carbon atoms exhibit unusual reactivity. Protonation of carbidic carbon in anions (4) addition of H2 to FeC(CO)122 under oxidising conditions (4) and carbide CO coupling (5) have been demonstrated. In general however knowledge pertinent to the patterns of reactivity for cluster bound unsaturated ligands is scarce despite an abundance of such data for mononuclear species. Our own efforts in the metal-cluster area have focused on an unsaturated moiety, the acetylide RCEC-,which, in its coordination chemistry_has features of similarity and contrast with CO and the carbides. The ethynyl anion HCEC: is isoelectronic with CO and like the latter has a polarised triple bond (6). Much of the early work on transition metal-acetylide coordination chemistry can be attributed to Nast and his co-workers who elegantly demonstrated the analogies between metal carbonyls and their anionic acetylide counterparts (7). Like CO, terminal and doubly bridging i2bonding modes for RCECare well known. For both ligands a variety of other bonding modes become accessible when the v-electrons of the CEO or RCECbonds are utilised (Scheme 1). Although examples of a-v-bonding of CO (eg. in Mn2 (CO)5(Ph2 113 I I 4 ARTHUR J . CARTY Scheme 1 Comparison of bonding modes for CmO and RCEC

An investigation of the reaction between [{Fe(η5–C5H5)(CO)2}2] and aryl isonitriles

The direct reaction between [{Fe(η5-C5H4X)(CO)2}2](X = H, Me, or COOMe) and aryl isonitriles RNC (R = 2,6-Me2C6H3 or C6H5) in refluxing toluene readily yields the tetrasubstituted derivatives [{Fe(η5-C5H4X)(RNC)2}2]. The intermediate derivatives [Fe2(η5-C5H5)2(CO)4–n(RNC)n](n= 1 or 2) can be prepared by the exchange reaction between [{Fe(η5-C5H5)(RNC)2}2] and [{Fe(η5-C5H5)(CO)2}2]. Reaction rates for the substitution of [{Fe(η5= C5H5X)(CO)2}2] by RNC are dependent on both the nature of R and X, and increase with both the nucleophilicity of R and the electron-withdrawing power of X. An alternative route to [Fe2(η5-C5H5)2(CO)4–n(RNC)n](n= 1 or 2) is via the reaction between Na[Fe(η5-C5H5)(CO)2] and 2,6-Me2C6H3NC in the presence of C7H7+BF4–. The isonitrile complexes have been characterized by i.r. and n.m.r. spectroscopy.

Carbon—carbon bond formation via coupling of isonitriles with μ 2-η 2-acetylides

The synthesis of carbon—carbon bonds via coupling of isonitriles RNC with the μ 2-η 2-acetylide in Fe 2(CO) 6(CCPh)(PPh 2)via nucleophilic attack at carbocationic carbon is described.

Metal carbonyl substitution reactions catalysed by transition metal complexes

The reaction of Fe(CO)5 with isonitriles RNC in the presence of CoCl2.2H2O as catalyst to give Fe(CO)5–n(RNC)n(n= 1–5) is reported.