Toward supramolecular assembly of 10-vertex { closo -2,1,10-FeC 2B7} clusters: Intramolecular Imidate Formation and Polymetallic, Polycluster Species

Article abstract of DOI:10.1021/om900970x

Addition of Me₃NO to CH₂Cl₂ solutions of [1-OH-2,2,2-(CO)₃-closo-2,1,10-FeC₂B₇H ₈] (1a) affords [2,2-(CO)₂-1,2-μ-{OCH ₂NMe₂}-closo-2,1,10-FeC₂B₇H ₈] (2), which contains a five-membered FeNCOC unit. The same reaction in MeCN as solvent gives [2,2-(CO)₂-1,2-μ-{OC(R)NH}-closo-2,1,10- FeC₂B₇H₈] (3a, R = Me). Analogous derivatives [R = CH - C(H)Me (3c), p-C₆H₄NO₂ (3d), p-C ₆H₄Br (3f), p-C₆H₄C(H)O (3g), p-C₆H₄C - CH (3h), p-C₅H₄N (3i), or NH₂ (3j)] are obtained from treatment of CH₂Cl₂ solutions of 1a with other cyano-containing substrates and Me₃NO. The μ-imidate species 3 undergo a variety of subsequent reactions. Thus, oxidative coupling of compound 3h in CH₂Cl₂, in the presence of CuCl-TMEDA (TMEDA = Me₂NCH₂CH ₂NMe₂), affords dimeric [2,2-(CO)₂-closo-2,1, 10-FeC₂B₇H₈-1,2-μ-{OC(N^FeH)-p- C₆H₄-C - C}]₂ (4), which reacts with [Co ₂(CO)₈] in CH₂Cl₂ to give the tetracluster species [2,2-(CO)₂-closo-2,1,10-FeC₂B ₇H₈-1,2-μ-{OC(N^FeH)-p-C₆H ₄-{(μ--²:-²-C - C)Co₂(CO) ₆}}]₂ (5). Conversely, 3f forms a bis(cluster) species, [2,2′-dppb-{2-CO-1,2-μ-{OC(C₆H₄Br)NH}-closo-2,1, 10-FeC₂B₇H₈}₂] (6), upon reaction with dppb (0.5 mol equiv) in refluxing THF (dppb = Ph₂P(CH ₂)₄PPh₂; THF = tetrahydrofuran). Compound 3a in CH₂Cl₂ with PHPh₂ and Me₃NO yields [2-CO-2-PHPh₂-1,2-μ-{OC(Me)NH}-closo-2,1,10-FeC₂B ₇H₈] (7), which, upon reaction with wet NEt₃ in CH₂Cl₂, gives [NHEt₃][2-CO-2-{P(O)Ph ₂}-1,2-μ-{OC(Me)NH}-closo-2,1,10-FeC₂B ₇H₈] (8). When a mixture of C₆H ₆-CH₂I₂ was used in the latter reaction, the product was [2-CO-2-PIPh₂-1,2-μ-{OC(Me)NH}-closo-2,1,10-FeC ₂B₇H₈] (9), which itself reacts with AgO ₂CMe, forming [2-CO-2-{P(O₂CMe)Ph₂}-1,2-μ- {OC(Me)NH}-closo-2,1,10-FeC₂B₇H₈] (10). Compound 3a reacts with excess [NBuⁿ₄]CN in CH ₂Cl₂ to form the anionic complex [1-OH-2,2-(CO) ₂-2-CN-closo-2,1,10-FeC₂B₇H₈] ^-, isolated as its [N(PPh₃)₂]⁺ salt (11), in which the intramolecular imidate portion of the precursor has been lost. The anion of 11 readily coordinates via the cyano group to the cationic {Ir(CO)(PPh₃)₂}⁺ fragment (formed from [IrCl(CO)(PPh₃)₂] and TlPF₆), affording [2-{(μ-CN)Ir(CO)(PPh₃)₂}-1-OH-2,2-(CO) ₂-closo-2,1,10-FeC₂B₇H₈] (12). Oxidative addition of MeI to the Ir(I) center in 12 gives the corresponding Ir(III) species [2-{(μ-CN)Ir(I)(Me)(CO)(PPh₃)₂}-1-OH-2, 2-(CO)₂-closo-2,1,10-FeC₂B₇H₈] (13). The novel structural features of these compounds - including hydrogen-bonding interactions - were confirmed by single-crystal X-ray diffraction studies.