Metal-Ligand Role Reversal: Hydride-Transfer Catalysis by a Functional Phosphorus Ligand with a Spectator Metal

Hydride transfer catalysis is shown to be enabled by the nonspectator reactivity of a transition metal-bound low-symmetry tricoordinate phosphorus ligand. Complex 1·[Ru]+, comprising a nontrigonal phosphorus chelate (1, P(N(o-N(2-pyridyl)C6H4)2) and an inert metal fragment ([Ru] = (Me5C5)Ru), reacts with NaBH4 to give a metallohydridophosphorane (1H·[Ru]) by P-H bond formation. Complex 1H·[Ru] is revealed to be a potent hydride donor (ΔG°H-,exp < 41 kcal/mol, ΔG°H-,calc = 38 ± 2 kcal/mol in MeCN). Taken together, the reactivity of the 1·[Ru]+/1H·[Ru] pair comprises a catalytic couple, enabling catalytic hydrodechlorination in which phosphorus is the sole reactive site of hydride transfer.

Different Schiff Bases-Structure, Importance and Classification

Schiff bases are a vast group of compounds characterized by the presence of a double bond linking carbon and nitrogen atoms, the versatility of which is generated in the many ways to combine a variety of alkyl or aryl substituents. Compounds of this type are both found in nature and synthesized in the laboratory. For years, Schiff bases have been greatly inspiring to many chemists and biochemists. In this article, we attempt to present a new take on this group of compounds, underlining of the importance of various types of Schiff bases. Among the different types of compounds that can be classified as Schiff bases, we chose hydrazides, dihydrazides, hydrazones and mixed derivatives such as hydrazide-hydrazones. For these compounds, we presented the elements of their structure that allow them to be classified as Schiff bases. While hydrazones are typical examples of Schiff bases, including hydrazides among them may be surprising for some. In their case, this is possible due to the amide-iminol tautomerism. The carbon-nitrogen double bond present in the iminol tautomer is a typical element found in Schiff bases. In addition to the characteristics of the structure of these selected derivatives, and sometimes their classification, we presented selected literature items which, in our opinion, represent their importance in various fields well.

Can chiral P(iii) coordinate Eu(iii)? Unexpected solvent dependent circularly polarised luminescence of BINAP and Eu(iii)(hfa)3 in chloroform and acetone

The coordination of Eu(iii) (from Eu(iii)(hfa)₃) by chiral P(iii) (from BINAP) led to circularly polarised luminescence in dilute solutions on the order of |g_em| ≈ 10⁻² at ⁵D₀ → F₁ and |g_em| ≈ 10⁻² at ⁵D₀ → F₂ transitions, i.e., in chloroform and acetone.

Zirconium complexes supported by an N-perfluoro-arylated diamidopyridyl ligand: synthesis of hydrazinediido complexes

The N-perfluoro-phenylated pyridyldiamine H2N2(PFP)N(py) (1) has been prepared by a palladium-catalyzed coupling of hexafluorobenzene and the diamine (H2NCH2)2C(CH3)(2-C5H4N) using the palladacycle trans-di(μ-acetato)bis[o-(di-o-tolylphosphino)benzyl]palladium(II) as catalyst. Reactions of H2N2(PFP)N(py) and Zr(NMe2)4 at room temperature or 90 °C led to the complexes [(N(PFP)N2(TFAP)N(py))ZrF(NMe2)] (2) and [(N2(TFAP)N(py))ZrF2] (3) in which one or two dimethylamido groups replaced one or two ortho fluorine atoms of the pentafluorophenyl groups in the ligand. Reaction of Me3SiX (X = Cl, I) with [(N2(TFAP)N(py))ZrF2] (3) resulted in the formation of mixed halogenated complexes [(N2(TFAP)N(py))ZrFI] (4) and [(N2(TFAP)N(py))ZrFCl] (5) in which the axially bound fluorido ligand is substituted. Reaction of [(N2(TFAP)N(py))ZrF2] (3) with LiNHNPh2 afforded the monohydrazido(1-) complex [(N2(TFAP)N(py))ZrF(NHNPh2)] (6) which was converted to the dimeric fluoro-potassium bridged hydrazinediido complex [Zr(N2(TFAP)N(py))FNNPh2K]2 (7) using KHMDS. The corresponding reaction with LiHMDS yielded the monomeric, donor free complex [Zr(N2(TFAP)N(py))NNPh2] (8).

Amino-functionalised diarylphosphide complexes of the alkali metals and lanthanum

The secondary phosphines Ar(C6H4-2-CH2NMe2)PH [Ar = mes (3), Tripp (4)] may be isolated in good yields from reactions between Li(C6H4-2-CH2NMe2) and the respective dichlorophosphine, followed by reduction with LiAlH4 [mes = 2,4,6-Me3C6H2, Tripp = 2,4,6-Pri3C6H2]. Metalation of either 3 or 4 with BunLi gives the corresponding lithium compound; the lithium derivative of 3 was isolated as the separated ion pair complex [Li(12-crown-4)2][(mes)(C6H4-2-CH2NMe2)P].THF (5). The lithium complexes Ar(C6H4-2-CH2NMe2)PLi undergo metathesis reactions with either NaOBut or KOBut to give the heavier alkali metal phosphides {Ar(C6H4-2-CH2NMe2)P}M.1/2OEt2 [Ar = mes, M = Na (8), K (9); Ar = Tripp, M = K (10)]. Metathesis reactions between 9 and LaI3(THF)4 give only intractable products; in contrast, a metathesis reaction between 10 and LaI3(THF)4 yields the heteroleptic complex {(Tripp)(C6H4-2-CH2NMe2)P}2LaI (11). Compound 11 reacts cleanly with K{N(SiMe3)2} to give {(Tripp)(C6H4-2-CH2NMe2)P}2La{N(SiMe3)2} (14). Compounds 3-5, 8-11 and 14 have been characterised by multi-element NMR spectroscopy; in addition, compounds 5, 11 and 14 have been studied by X-ray crystallography.

Lanthanide-Mediated Ligand Transfer Reactions—A Route to Late Transition Metal Bisamido Complexes

The reaction of [[O(SiMe2Ap)2)2LnLi(thf)n] 1 (Ln = Nd, n= 2) and 2 (Ln = La, n = 3) in hexane with [(dme)NiCl2] (dme = dimethoxyethane) and [(cod)PtCl2] (cod = 1,5-cyclooctadiene) leads to the dimeric Ni complex [[O(SiMe2Ap)2]2Ni2] (3) and the mononuclear platinum compound [O(SiMe2Ap)2Pt] (4). respectively (O(SiMe2ApH)2 = bis(4-methyl-2-pyridylamino)tetramethyldisiloxane). Compounds 3 and 4 have been characterized by X-ray crystal structure analysis. The ligand-transfer reactions probably proceed via heterobimetallic intermediates. A model complex of such an intermediate [[O(SiMe2Ap)2)2NdPdMe] (7) was isolated by reacting 1 with [(cod)PdMeCl]. Applications of complex 3 in ethylene oligomerization were investigated. Highly branched oligomers with a very narrow molecular weight distribution (Mn =230 gmol(-1) (relative to polystyrene standards), Mw/M= 1.14) are produced when Et3Al2Cl3 is employed as a co-catalyst and CH2Cl2 as the solvent (TOF = 122000 h(-1). Treatment of one equivalent of 1 or 2 with two equivalents of [(cod)CuCl] results in the formation of the polycyclic tetranuclear complex [[O(SiMe2Ap)2]2Cu4] (8). An X-ray crystal structure analysis of 8 shows channels formed by a series of fourteen-membered rings in the solid state.

Synthesis and Structure of a New Lithium Amide Ligand Precursor: A Tridentate Nitrogen-Based Donor Set of the Formula N(SiMe(2)CH(2)NMe(2))(2). Synthesis and Structure of the Group 4 Amides MCl(3)[N(SiMe(2)CH(2)NMe(2))(2)] (M = Ti, Zr, Hf)

The new lithium amide LiN(SiMe(2)CH(2)NMe(2))(2) was prepared by reaction of NH(3) with the corresponding silylamine Me(2)NSiMe(2)CH(2)NMe(2) followed by addition of butyllithium. This lithium derivative exists as a dimer in the solid state wherein the two lithium ions are bridged by the two amido units with the amine arms of each unit bonded to opposite lithium centers in an overall pseudo D(2) structure; however, in solution, a fluxional process serves to interconvert the enantiomeric forms of the dimer unit. The coordination chemistry of the lithium amide dimer has been investigated; reaction with a series of group 4 starting halides, MCl(4), leads to the corresponding complexes MCl(3)[N(SiMe(2)CH(2)NMe(2))(2)], where M = Ti, Zr, and Hf. The structures of these starting trihalides in solution and in the solid state are presented.