1′-(Diphenylphosphino)-1-isocyanoferrocene (1) was prepared as a hybrid ligand for Ag(i) and Au(i) complexes; the catalytic activity of the Au(i) complexes was studied.
Removal of the chloride ligand from [AuCl(1-κP)] (2) containing a P-monodentate 1'-(diphenylphosphanyl)-1-cyanoferrocene ligand (1), by using silver(I) salts affords cationic complexes of the type [Au(1)]X, which exist either as cyclic dimers [Au(1)]2 X2 (3 a, X=SbF6 ; 3 c, X=NTf2 ) or linear coordination polymers [Au(1)]n Xn (3 a', X=SbF6 ; 3 b', X=ClO4 ), depending on anion X and the isolation procedure. As demonstrated for 3 a', the polymers can be readily cleaved by the addition of donors, such as Cl(-) , tetrahydrothiophene (tht) or 1, giving rise to the parent compound 2, [Au(tht)(1-κP)][SbF6 ] (5 a) or [Au(1-κP)2 ][SbF6 ] (4 a), respectively, of which the last two compounds can also be prepared by stepwise replacement of tht in [Au(1-κP)2 ][SbF6 ]. The particular combination of a firmly coordinated (phosphane) and a dissociable (nitrile) donor moieties renders complexes 3/3' attractive for catalysis because they can serve as shelf-stable precursors of coordinatively unsaturated Au(I) fragments, analogous to those that result from the widely used [Au(PR3 )(RCN)]X catalysts. The catalytic properties of the Au-1 complexes were evaluated in model annulation reactions, such as the synthesis of 2,3-dimethylfuran from (Z)-3-methylpent-2-en-4-yn-1-ol and oxidative cyclisation of alkynes with nitriles to produce 2,5-disubstituted 1,3-oxazoles. Of the compounds tested (2, 3 a', 3 b', 3 a, 4 a and 5 a), the best results were consistently achieved with dimer 3 c, which has good solubility in organic solvents and only one firmly bound donor at the gold atom. This compound was advantageously used in the key steps of annuloline and rosefuran syntheses.
1'-(Diphenylphosphino)-1-cyanoferrocene () reacts with silver(i) halides at a 1 : 1 metal-to-ligand ratio to afford the heterocubane complexes [Ag(μ3-X)(-κP)]4, where X = Cl (), Br (), and I (). In addition, the reaction with AgCl with 2 equiv. of leads to chloride-bridged dimer [(μ-Cl)2{Ag(-κP)2}2] () and, presumably, also to [(μ(P,N)-){AgCl(-κP)}]2 (). While similar reactions with AgCN furnished only the insoluble coordination polymer [(-κP)2Ag(NC)Ag(CN)]n (), those with AgSCN afforded the heterocubane [Ag(-κP)(μ-SCN-S,S,N)]4 () and the thiocyanato-bridged disilver(i) complex [Ag(-κP)2(μ-SCN-S,N)]2 (), thereby resembling reactions in the AgCl- system. Attempted reactions with AgF led to ill-defined products, among which [Ag(-κP)2(μ-HF2)]2 () and [(μ-SiF6){Ag(-κP)2}2] () could be identified. The latter compound was prepared also from Ag2[SiF6] and . Reactions between and AgClO4 or Ag[BF4] afforded disilver complexes [(μ(P,N)-)Ag(ClO4-κO)]2 () and [(μ(P,N)-)Ag(BF4-κF)]2 () featuring pseudolinear Ag(i) centers that are weakly coordinated by the counter anions. A similar reaction with Ag[SbF6] followed by crystallization from ethyl acetate produced an analogous complex, albeit with coordinated solvent, [(μ(P,N)-)Ag(AcOEt-κO)]2[SbF6]2 (). Ultimately, a compound devoid of any additional ligands at the Ag(i) centers, [(μ(P,N)-)Ag]2[B(C6H3(CF3)2-3,5)4]2 (), was obtained from the reaction of with silver(i) tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. The reaction of Ag[BF4] with two equivalents of produced unique coordination polymer [Ag(-κP)(μ(P,N)-)]n[BF4]n (), the structure of which contained one of the phosphinoferrocene ligands coordinated as a P,N-chelate and the other forming a bridge to an adjacent Ag(i) center. All of these compounds were structurally characterized by single-crystal X-ray crystallography, revealing that the lengths of the bonds between silver and its anionic ligand(s) typically exceed the sum of the respective covalent radii, which is in line with the results of theoretical calculations at the density-functional theory (DFT) level, suggesting that standard covalent dative bonds are formed between silver and phosphorus (soft acid/soft base interactions) while the interactions between silver and the ligand's nitrile group (if coordinated) or the supporting anion are of predominantly electrostatic nature.
1'-(Diphenylphosphino)-1-cyanoferrocene (3), a new donor-asymmetric ferrocene ligand obtained in two steps from 1'-(diphenylphosphino)ferrocene-1-carboxaldehyde, reacts with CuCl at a Cu/3 molar ratio of 1:1 to give the heterocubane complex [Cu(μ3-Cl)(3-κP)]4 (4). When the Cu/3 ratio is changed to 1:2 or 1:3, the reaction takes a different course, producing the P,N-bridged dimer [CuCl(3-κP)(μ(P,N)-3)]2 (5) after crystallization. Notably, CuBr and CuI behave differently, affording the corresponding 2D coordination polymers [CuX(μ(P,N)-3)]n [X = I (7), and Br (8)], regardless of the Cu/3 ratio. Reaction of 3 with sources of naked Cu(+), such as [Cu(MeCN)4](+) salts or their synthetic equivalents, provides the 1D coordination polymer [Cu(MeCN-κN)(μ(P,N)-3)][BF4] (9) or salts of a quadruply bridged dicopper(I) cation, [Cu2(μ(P,N)-3)4]X2 ([10]X2), depending on the Cu/3 molar ratio (1:1 vs 1:2 and 1:3). Except for 4, in which 3 binds as a simple P-monodentate ligand, the complexes reported here represent the first structurally characterized compounds in which a phosphinonitrile ligand coordinates through both of its soft donor moieties, thereby extending the coordination chemistry of these ligands.
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