Pnictogen-Functionalised C1 Ligands: MC-ARn (n=0, 1, 2, 3).

The chemistry of transition metal carbynes, Ln M≡CR, has historically been dominated by species bearing hydrocarbyl or amino 'R' substituents, with other elements appearing only sporadically. In recent years, carbynes and related 'C1 ' species bearing other main-group substituents, particularly heavier elements of the p-block, have begun to emerge. This review details the chemistry of heavier pnictogen-functionalised C1 ligands, MCARn (A=P, As, Sb, Bi; n=0-3), including their syntheses, properties and reactivities, and how these are distinguished from more traditional carbyne complexes. Recent developments in the closely related phospha-isonitrile Ln M(CPR), cya-phosphide and cya-arside ligands, Ln M(C≡A) (A=P, As), are also discussed.

Propargylidyne and Pentadiynylidyne Polyfunctionalised Polycyclic Aromatic Hydrocarbons.

The Pd0 /AuI mediated [C1 +C2 ] cross-coupling reactions of [W(≡CBr)(CO)2 (Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) and trimethylsilylethynyl-substituted arenes afford new polycyclic aromatic hydrocarbon propargylidynes [W(≡CC≡CR)(CO)2 (Tp*)] (R=9-anthracenyl, 1-pyrenyl). The strategy extends to the first bis(propargylidyne) and bis(pentadiynylidyne) complexes bridged by phenyl or anthracenyl spacers, and to a tetrakis(propargylidyne) connected through a pyrene core.

Advances in Transition Metal Seleno- and Tellurocarbonyl Chemistry.

In contrast to the ubiquity of transition-metal carbonyl, and (to a lesser extent) thiocarbonyl complexes, transition-metal complexes of carbon monoselenide Ln MCSe and monotelluride Ln MCTe remain scarce. The last few years, however, have seen notable steps towards expanding this chemistry, specifically with regards to new systematic studies on homologous sets of chalcocarbonyl complexes Ln MCE (E=O, S, Se, Te), the first reports of new bi- and polynuclear CSe and CTe bridging complexes and a confluence with metal carbido chemistry. Herein the properties, syntheses and reactions of these rare but fundamentally intriguing compounds are discussed.

In Search of Fulminate Analogues: Ln M≡CP=NR.

The "CPNR" ligand may be viewed as being isolobal with fulminate, CNO; however, attempts to prepare a complex of such a ligand resulted instead in a range of novel imino and aminophosphinocarbyne complexes. Sequential treatment of [Mo(≡CBr)(CO)2 (Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) with nBuLi and ClP=NMes* (Mes*=C6 H2 tBu3 -2,4,6) afforded mixtures of the complexes [Mo(≡CPnBuNHMes*)(CO)2 (Tp*)] and traces of the bimetallic products [Mo2 {µ2 -C2 P2 O(NHMes)2 }(CO)4 (Tp*)2 ] and [Mo2 (µ2 -C2 PNHMes)(CO)4 (Tp*)2 ]. The reaction of [W(≡CBr)(CO)2 (Tp*)] with nBuLi and ClP=NMes* afforded predominantly the mononuclear carbyne [W{≡CP(=NMes*)nBu2 })(CO)2 (Tp*)] and traces of the binuclear complex [W2 (µ-C2 PNHMes)(CO)4 (Tp*)2 ] which is also obtained when tBuLi is used. Although not isolable, the intended complexes [M(≡CPNMes*)(CO)2 (Tp*)] could be generated in situ and spectroscopically characterized via the reactions of the stannyl carbynes [M(≡CSnnBu3 )(CO)2 (Tp*)] and ClP=NMes*. The preceding observations are mechanistically interpreted with reference to a computational interrogation of the model complex [Mo(≡CP=NCH3 )(CO)2 (Tp*)], the LUMO of which has considerable phosphorus character.

Flexible Platinum(0) Coordination to a Ditungsten Ethanediylidyne.

The lithiocarbyne [W(≡CLi)(CO)2 (Tp*)] (Tp*=hydrotris(3,5-dimethylpyrazol-1-yl)borate) reacts with [PtCl2 (L2 )] (L2 =1,5-cyclo-octadiene, norbornadiene) to furnish ditungsten ethanediylidyne complexes, [W2 {µ-C2 Pt(L2 )}(CO)4 (Tp*)2 ], wherein a trigonal platinum(0) center unsymmetrically ligates one W≡C bond in the solid state but rapidly shimmies between the two W≡C bonds in solution. The η4 -dienes are displaced by monodentate CO or isocyanide ligands to provide derivatives where both W≡C bonds coordinate to a single Pt0 center, attended by significant distortion of the WCCW spine.

Bi- and Polynuclear Transition-Metal Carbon Tellurides.

The first examples of bi- and polynuclear tellurocarbonyl complexes were obtained from the reactions of [W(≡CTe)(CO)2 (Tp*)]NEt4 (Tp*=hydrotris(dimethylpyrazolyl)borate) with [MCl(PCy3 )]/TlPF6 (M=Cu, Au) or [Au2 Cl2 (µ-dppm)], which afford [WM(µ-CTe)(PCy3 )(CO)2 (Tp*)] (M=Cu, Au) and [WAu2 (µ-CTe)(µ-dppm)(CO)2 (Tp*)]3 (PF6 )3 . In all cases it is specifically the tellurocarbonyl that assumes a bridging, but in each case distinct, role including examples of isotellurocarbonyl, semi-bridging and σ-π coordination and combinations thereof. Tetrametallic complexes bridged by C2 Te and C2 Te2 ligands are also described.

Tetrahedral Pegs in Square Holes: Stereochemistry of Diboron Porphyrazines and Phthalocyanines.

The first examples of diboron complexes of the tetrapyrroles octaethylporphyrazine (OEPz) and 2,9,16,23-tetra-t-butyl-phthalocyanine (Pc) are reported, counterpoints to the better known monoboron tripyrroles, subporphyrazine and subphthalocyanine. Two stereochemical possibilities are observed, with cisoid-B2 OF2 (OEPz), both cisoid-B2 OPh2 (OEPz) and transoid-B2 OPh2 (OEPz), transoid-B2 OF2 (Pc) and cisoid-B2 OPh2 (Pc) having been isolated and characterised, including structure determinations for the OEPz complexes. This variation in stereochemistry, which can be extended to include the previously reported transoid-B2 OF2 (porphyrin), cisoid-[B2 OF2 (corrole)]- , and both transoid- and cisoid-B2 OF2 (calixphyrin), prompted a wider DFT study to elucidate the factors influencing the stereochemical preferences. This shows that the cisoid/transoid preference is correlated to the ease with which the macrocycle accommodates a rectangularly distorted N4 cavity.

Recent Advances in Metallaaromatic Chemistry.

Metallaaromatics can be broadly defined as aromatic compounds in which one of the ring atoms is a transition metal. The metallabenzenes are one important class of these compounds that has undergone extensive study recently. Closely related species such as fused-ring metallabenzenes, heterometallabenzenes, π-coordinated metallabenzenes and metallabenzynes have also attracted considerable attention. Although many metallaaromatics can be considered as metalla-analogues of classic organic aromatic compounds, this is not always the case. Recent seminal studies have shown that metallapentalenes and metallapentalynes, which are metalla-analogues of the anti-aromatic compounds pentalene and pentalyne, are in fact aromatic and highly stable. Very unusual spiro-metallaaromatic compounds have also recently been isolated. In this concepts article, key features of all these intriguing metallaaromatic compounds are discussed with reference to the structural, spectroscopic, reactivity and theoretical studies that have been undertaken. These compounds continue to generate much interest, not only because of the contributions they make to fundamental chemical understanding, but also because of the promise of possible practical applications.

Syntheses of Amino-Substituted Iridabenzofurans and Subsequent Selective N-Functionalisation.

The first examples of amino-substituted fused-ring metallabenzenes, the cationic iridabenzofuran [Ir(C7 H4 O{NH2 -2}{OMe-7})(CO)(PPh3 )2 ][O3 SCF3 ] (5) and neutral analogue Ir(C7 H4 {NH2 -2}{OMe-7})Cl(PPh3 )2 (6), can be prepared by reduction of the corresponding nitro-substituted iridabenzofurans with zinc and concentrated hydrochloric acid. N-functionalised derivatives of 5 and 6 are formed through alkylation, sulfonylation or acylation. Thus, consecutive treatments with methyl triflate and base gives the corresponding trimethylammonium-substituted iridabenzofurans while sulfonamide derivatives are formed with p-toluenesulfonyl chloride. N-Acylation of 5 or 6 with acid chlorides, however, selectively form either amide or imide products depending on the charge on the metal and the steric size of the acid chloride. Cationic 5 gives amide substituted products regardless of the conditions whereas neutral 6 rapidly undergoes di-N-acylation with excess benzoyl chloride under mild conditions to give the imide-substituted product Ir(C7 H4 O{N[C(O)Ph]2 -2}{OMe-7})Cl(PPh3 )2 (13). Selective mono-acylation of 6 can be achieved with one equivalent of benzoyl chloride or with excess of the sterically congested pivaloyl chloride.

A Metallaanthracene and Derived Metallaanthraquinone.

Metalla-analogues of archetypal aromatic molecules are attracting ever increasing interest. Although metallabenzenes (which fall within this class) have been well studied, fused-ring metallabenzenes are rare and of the linear polycyclic metallaaromatic hydrocarbons, only metallanaphthalene is known. Herein we report the first metallaanthracene, [Ir(C13 H8 {CH2 CO2 Me-5})Cl(PPh3 )2 ]O3 SCF3 (5), which represents the next member of this series of polycyclic compounds. Structurally, 5 has a number of features in common with anthracene including fused-ring planarity and bond-length alternation. In analogues of classic reactions of anthracene, 5 forms a Diels-Alder adduct with maleic anhydride and on oxidation the unprecedented fused-ring metallaanthraquinone, [Ir(C15 H6 O{Br-6}{OMe-7}{=O-8}{=O-15})Br(PPh3 )2 ], is obtained.

Synthesis and reactivity of 9,10-bis(4-trimethylsilylethynylbuta-1,3-diynyl)anthracene derived chromophores.

9,10-Bis(4-trimethylsilylethynylbutadiynyl)anthracene is readily availabe from the reaction of anthraquinone and LiCCCCSiMe3 followed by reduction with Sn(II) and serves as a convenient building block via desilylation and palladium-mediated C-C coupling processes for the construction of further butadiynylanthracenes terminated by metal complexes, arenes, haloarenes and alkynyl functionalities.

Arsinocarbyne reactivity.

The reactivity of the tungsten diphenylarsinocarbyne [W(CAsPh2)(CO)2(Tp*)] (1; Tp* = hydrotris(dimethylpyrazolyl)borato) is described. The pyramidal arsenic coordinates to a selection of 5d metal centres, forming heterobi- or trimetallic complexes with osmium(II), iridium(III), platinum(II) and gold(I). In the latter case, the WC bond provides a competitive site for gold(I) coordination. Treatment with MeOSO2CF3 results in methylation at arsenic to give the first example of an arsoniocarbyne, [W(CAsPh2CH3)(CO)2(Tp*)]O3SCF3, for which only the WC bond remains available for gold(I) coordination.

Organometallic flow chemistry: solvento complexes.

Photolysis under optimised flow conditions of metal carbonyls [{Ln}M(CO)x] [{Ln}M(CO)x = Cr(CO)6, Mo(CO)6, W(CO)6, Mn(CO)3(η-C5H4Me), Re(CO)3(η-C5H5)] in tetrahydrofuran (THF) conveniently affords the synthetically versatile and labile solvento complexes [{Ln}M(CO)x-1(THF)], thereby obviating many of the caveats associated with photochemical syntheses using either 'batch' or falling film techniques. Conversions were optimised and yields assayed by a combination of in situ infrared spectroscopy and derivatisation as the corresponding triphenylphosphine complexes [{Ln}M(CO)x-1(PPh3)].

Symmetric and non-symmetric anthracen-diyl bis(alkylidynes).

Three examples of 9-bromo-10-(alkylidynyl)anthracenes, [W{CC(C6H4)2CBr}(CO)2(L)] (L = hydrotris(dimethylpyrazol-1-yl)borate Tp*, hydrotris(pyrazol-1-yl)borate Tp, hydrotris(2-mercapto-N-methylimidazol-1-yl)borate Tm) were prepared via modified Fischer-Mayr acyl oxide-abstraction protocols. With a sufficiently bulky ancillary ligand (L = Tp*) the aryl bromide is ammenable to cross-coupling reactions that enable more elaborate derivatives to be prepared. These including symmetric bis(alkylidynyl)anthracenes as well as non-palindromic examples bearing disparate metals and/or co-ligands. In contrast, these couplings fail for smaller ligands (L = Tp, Tm) where it was found that Pd0 or Pt0 were instead able to coordinate across two WC bonds to give trimetallic bow-tie complexes, [W2M{µ-CC(C6H4)2CBr}2(CO)4(L)2] (M = Pd, Pt; L = Tp, Tm).

Bimetallic ethynylanthracenyl functionalised carbynes.

Mono- and bimetallic anthracenes functionalised by alkynyl and alkylidynyl substituents are obtained via sequential cross-coupling reactions of the 9-bromoanthracenyl carbyne [W{CC(C6H4)2CBr}(CO)2(Tp*)].

Heterocyclic arsinocarbynes via tandem transmetallation.

Gold(i)-catalysed tandem transmetallation (Sn→Au→As) of the stannylcarbyne [W(≡CSnnBu3)(CO)2(Tp*)] (Tp* = hydrotris-(dimethylpyrazolyl)borate) with haloarsines gives direct access to a range of novel arsinocarbyne complexes, LnM≡CAsR2, including unusual heterocyclic phenarsazininyl and arsolyl examples.

Metal coordination to bipyridyl carbynes.

The Pd0/AuI-mediated coupling of the stannylcarbyne [W([triple bond, length as m-dash]CSnnBu3)(CO)2(Tp*)] (1) and 6-bromo-2,2'-bipyridine or 6,6'-dibromo-2,2'-bipyridine gives new carbynes functionalised on the carbyne carbon(s) with a bipyridyl group. These new 'metallo-ligands' undergo protonation at the pyridyl nitrogens, metallation of the tungsten-carbon triple bond with [AuCl(SMe2)], and metallation of the bipyridyl moiety with K[PtCl3(C2H4)]·H2O, [ReBr(CO)5] and [MCl(COD]2 (M = Ir, Rh; COD = η4-cycloocta-1,5-diene).

Carbyne decorated porphyrins.

The Pd0/AuI-mediated coupling between stannylcarbyne [W([triple bond, length as m-dash]CSnnBu3)(CO)2(Tp*)] (1) and meso-5,10,15,20-tetrakis(3' or 4'-bromophenyl)porphyrins gives tetrametallic derivatives where a central porphyrin unit is formally substituted at the four meso positions by tungsten benzylidyne moieties. These new 'metallo-porphyrins' undergo metallation at the porphyrin centres with Zn(OAc)2·2H2O to give a pentametallic W4Zn complex or at the tungsten-carbon triple bonds with [AuCl(SMe2)] to give an octametallic W4Au4 complex. The Zn(ii)-metalloporphyrin derivatives are capable of reversibly coordinating further axial ligands such as 4-dimethylaminopyridine or meta-pyridylcarbynes, which themselves are prepared via a coupling between 1 and the appropriate (di)bromopyridine.

Bi- and poly(carbyne) functionalised polycyclic aromatics.

Complexes where a central polyaromatic ring system is substituted with one to four tungsten carbynes have been prepared by Pd0/AuI-mediated coupling between a tungsten stannylcarbyne and aryl halides. This strategy enables preparation of complexes with one to three carbynes substituted onto a single phenyl ring, the first anthracenyl mono- and bis-carbynes, and a tetra(carbyne) complex constructed about a central pyrene ring system.

Semi-bridging σ-silyls as Z-type ligands.

The reactions of SiHPh(NCH2PPh2)2C6H4-1,2 with a range of zerovalent group 10 reagents afford the homoleptic bimetallic complexes [M2{µ-κ3-Si,P,P'-SiPh(CH2PPh2)2C6H4}2] (M = Ni, Pd, Pt) in which the M-M bond is unsymmetrically bridged by two σ-silyl groups. The asymmetry of the M2Si2 core increases from Ni through Pd to Pt and is consistent with a bonding description in which one metal acts as an electron pair donor to a trigonal bipyramidal 'Z-type' silicon centre, reminsicent of semi-bridging coordination by CO, carbynes and boryl ligands.