A Monometallic Bis(cyaphido) Complex

The first example of a bis(cyaphido) complex, trans-[Ru(dppe)2(C≡P)2], is described, unequivocally demonstrating the synthetic accessibility and stability of complexes that feature more than one cyaphido ligand. Synthesis is achieved from the precedent cation [Ru(dppe)2(C≡P)]+ via sequential coordination and desilylation of the phosphaalkyne Me3SiC≡P. The heteroleptic analogue trans-[Ru(dppe)2(C≡N)(C≡P)] is also prepared from the same cation and NaCN; both cyaphido complexes are structurally characterized, enabling the first direct comparison of cyaphide with cyanide, its isoelectronic and isolobal counterpart. This demonstrates an enhanced π-acidity for -C≡P over -C≡N, while computational studies reveal also a higher π-donor character for the cyaphido ligand.

Isonitrile μ2-carbido complexes

The μ-carbido complex [WPt(μ-C)Br(CO)2(PPh3)2(Tp*)] (Tp = hydrotris(dimethylpyrazolyl)borate) undergoes substitution of one phosphine ligand with isonitriles to afford complexes [WPt(μ-C)Br(CNR)(CO)2(PPh3)(Tp*)] (R = tBu, C6H3Me2-2,6, C6H2Me3-2,4,6). For aryl but not alkyl isocyanides disubstitution follows to afford [WPt(μ-C)Br(CNR)2(CO)2(Tp*)] (R = C6H2Me2-2,6, C6H2Me3-2,4,6). The bis(isonitrile) derivatives, including [WPt(μ-C)Br(CNtBu)2(CO)2(Tp*)], may also be prepared from the reactions of triangulo-[Pt3(CNR)6] with [W(CBr)(CO)2(Tp*)]. Bis- and tris(dimethylpyrazolyl)borate pro-ligand salts replace the bromide and one phosphine in [WPt(μ-C)Br(CNC6H2Me3)(CO)2(PPh3)(Tp*)] or the bromide and one isonitrile in [WPt(μ-C)Br(CNC6H2Me3)2(CO)2(Tp*)] to afford [WPt(μ-C)(CNC6H2Me3)(CO)2(Tp*)(L)] (L = κ2-Tp*, dihydrobis(pyrazolyl)borate). Structural, spectroscopic and computational data for the complexes are discussed to interrogate the nature of the WC-Pt carbido bridge by analogy with a range of other sp-C1 and sp-B1 ligands (CN, CCH, CP, CAs, CSb, CNO, BO, BNH and BCH2).

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.

Photochemical C(sp)-C(sp2) Bond Activation in Phosphaalkynes: A New Route to Reactive Terminal Cyaphido Complexes LnM-C≡P

The photochemical activation of the C(sp)-C(sp²) bond in Pt(0)-η²-aryl-phosphaalkyne complexes leads selectively to coordination compounds of the type L_nPt(aryl)(C≡P). The oxidative addition reaction is a novel, clean, and atom-economic route for the synthesis of reactive terminal Pt(II)-cyaphido complexes, which can undergo [3 + 2] cycloaddition reactions with organic azides, yielding the corresponding Pt(II)-triazaphospholato complexes. The C-C bond cleavage reaction is thermodynamically uphill. Upon heating, the reverse and quantitative reductive elimination toward the Pt(0)-phosphaalkyne-π-complex is observed.

Controlled Reactivity of Terminal Cyaphide Complexes: Isolation of the 5-Coordinate [Ru(dppe)2(C≡P)]. Inorg Chem 2019;58:14800-14807. [PMID: 31633922 DOI: 10.1021/acs.inorgchem.9b02471]

The novel cyaphide complex trans-[Ru(dppe)₂Me(C≡P)] is obtained in excellent yields and exhibits the first instance of controlled reactivity of any terminal cyaphide complex. Its treatment with ZnX₂/PPh₃ effects selective metathesis of the methyl moiety to afford the unprecedented halocyaphide complexes trans-[Ru(dppe)₂(X)(C≡P)] (X = Cl, Br, I), which are structurally characterized (X = Cl, Br). Exemplified with the trans-bromide, these compounds are susceptible to substitution of the halides by nucleophilic reagents-illustrated with Me₂Mg-and also readily undergo halide abstraction by TlOTf to afford the first hypocoordinate cyaphide complex, viz., [Ru(dppe)₂(C≡P)]·OTf, which is isolable in bulk and exhibits good stability. NMR spectroscopic and crystallographic data reveal the latter to adopt a square-pyramidal geometry with an accessible coordinate vacancy, which is susceptible to the addition of nucleophiles. This is illustrated analytically by reactions with Me₂Mg and LiC≡CPh and with its facile bulk carbonylation to afford trans-[Ru(dppe)₂(CO)(C≡P)]⁺.