The first adducts of NHCs (= N-heterocyclic carbenes) with aromatic polyphosphorus complexes are reported. The reactions of [Cp*Fe(h 5-P 5)] (1)(Cp* = pentamethyl-cyclopentadienyl) with IMe (= 1,3,4,5-tetramethylimidazolin-2-ylidene), IMes (= 1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene) and IDipp (= 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) led to the corresponding neutral adducts which can be isolated in the solid state. However,i ns olution,t hey quicklyu ndergo ad issociative equilibrium between the adduct and 1 including the corresponding NHC. The equilibrium is influencedb yt he bulkiness of the NHC. [Cp''Ta (CO) 2 (h 4-P 4)] (Cp'' = 1,3-di-tertbutylcyclopentadienyl) reacts with IMe under Pa tom abstraction to give an unprecedented cyclo-P 3-containing anionic tantalum complex.D FT calculations shed light onto the energetics of the reaction pathways.
The rational synthesis of dinuclear asymmetric phosphanido derivatives of palladium and platinum(II), [NBu(4)][(R(F))(2)M(μ-PPh(2))(2)M'(κ(2),N,C-C(13)H(8)N)] (R(F) = C(6)F(5); M = M' = Pt, 1; M = Pt, M' = Pd, 2; M = Pd, M' = Pt, 3; M = M' = Pd, 4), is described. Addition of I(2) to 1-4 gives complexes [(R(F))(2)M(II)(μ-PPh(2))(μ-I)Pd(II){PPh(2)(C(13)H(8)N)}] (M = M' = Pt, 6; M = Pt, M' = Pd, 7; M = M' = Pd, 8; M = Pd, M' = Pt 10) which contain the aminophosphane PPh(2)(C(13)H(8)N) ligand formed through a Ph(2)P/C^N reductive coupling on the mixed valence M(II)-M'(IV) [NBu(4)][(R(F))(2)M(II)(μ-PPh(2))(2)M'(IV)(κ(2),N,C- C(13)H(8)N)I(2)] complexes, which were identified for M(II) = Pd, M'(IV) = Pt (9), and isolated for M(II) = Pt, M'(IV) = Pt (5). Complex 5 showed an unusual dynamic behavior consisting in the exchange of two phenyl groups bonded to different P atoms, as well as a "through space" spin-spin coupling between ortho-F atoms of the pentafluorophenyl rings.
Two Co(I) hydrides containing the tripodal polyphosphine ligand EP, (κ-EP)Co(H) [E(CHCHPPh); E = N (1), P (2)], have been exploited as ammonia borane (NHBH, AB) dehydrogenation catalysts in THF solution at T = 55 °C. The reaction has been analyzed experimentally through multinuclear (B, P{H}, H) NMR and IR spectroscopy, kinetic rate measurements, and kinetic isotope effect (KIE) determination with deuterated AB isotopologues. Both complexes are active in AB dehydrogenation, albeit with different rates and efficiency. While 1 releases 2 equiv of H per equivalent of AB in ca. 48 h, with concomitant borazine formation as the final "spent fuel", 2 produces 1 equiv of H only per equivalent of AB in the same reaction time, along with long-chain poly(aminoboranes) as insoluble byproducts. A DFT modeling of the first AB dehydrogenation step has been performed, at the M06//6-311++G** level of theory. The combination of the kinetic and computational data reveals that a simultaneous B-H/N-H activation occurs in the presence of 1, after a preliminary AB coordination to the metal center. In 2, no substrate coordination takes place, and the process is better defined as a sequential BH/NH insertion process on the initially formed [Co]-NHBH amidoborane complex. Finally, the reaction of 1 and 2 with NH-acids [AB and MeNHBH (DMAB)] has been followed via VT-FTIR spectroscopy (in the -80 to +50 °C temperature range), with the aim of gaining a deeper experimental understanding of the dihydrogen bonding interactions that are at the origin of the observed H evolution.
The reactivity of the dinuclear platinum(III) derivative [(R(F))2Pt(III)(μ-PPh2)2Pt(III)(R(F))2](Pt-Pt) (R(F) = C6F5) (1) toward OH(-), N3(-), and NCO(-) was studied. The coordination of these nucleophiles to a metal center evolves with reductive coupling or reductive elimination between a bridging diphenylphosphanido group and OH(-), N3(-), and NCO(-) or C6F5 groups and formation of P-O, P-N, or P-C bonds. The addition of OH(-) to 1 evolves with a reductive coupling with the incoming ligand, formation of a P-O bond, and the synthesis of [NBu4]2[(R(F))2Pt(II)(μ-OPPh2)(μ-PPh2)Pt(II)(R(F))2] (3). The addition of N3(-) takes place through two ways: (a) formation of the P-N bond and reductive elimination of PPh2N3 yielding [NBu4]2[(R(F))2Pt(II)(μ-N3)(μ-PPh2)Pt(II)(R(F))2] (4a) and (b) formation of the P-C bond and reductive coupling with one of the C6F5 groups yielding [NBu4][(R(F))2Pt(II)(μ-N3)(μ-PPh2)Pt(II)(R(F))(PPh2R(F))] (4b). Analogous behavior was shown in the addition of NCO(-) to 1 which afforded [NBu4]2[(R(F))2Pt(II)(μ-NCO)(μ-PPh2)Pt(II)(R(F))2] (5a) and [NBu4][(R(F))2Pt(II)(μ-NCO)(μ-PPh2)Pt(II)(R(F))(PPh2R(F))] (5b). In the reaction of the trinuclear complex [(R(F))2Pt(III)(μ-PPh2)2Pt(III)(μ-PPh2)2Pt(II)(R(F))2](Pt(III)-Pt(III)) (2) with OH(-) or N3(-), the coordination of the nucleophile takes place selectively at the central platinum(III) center, and the PPh2/OH(-) or PPh2/N3(-) reductive coupling yields the trinuclear [NBu4]2[(R(F))2Pt(II)(μ-Ph2PO)(μ-PPh2)Pt(II)(μ-PPh2)2Pt(II)(R(F))2] (6) and [NBu4][(R(F))2Pt(1)(μ3-Ph2PNPPh2)(μ-PPh2)Pt(2)(μ-PPh2)Pt(3)(R(F))2](Pt(2)-Pt(3)) (7). Complex 7 is fluxional in solution, and an equilibrium consisting of Pt-Pt bond migration was ascertained by (31)P EXSY experiments.
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