Beiträge zur Chemie des Phosphors. 159. Über die Reaktion des Diphosphaborirans (t-BuP)2BN(i-Pr)2 mit Kalium bzw. Kaliumnaphthalid

Contributions to the Chemistry of Phosphorus. 159. On the Reaction of the Diphosphaborirane (t-BuP)₂BN(i-Pr)₂ with Potassium or Potassium Naphthalenide The reaction of (t-BuP)₂BN(i-Pr)₂ with potassium or K-naphthalenide in tetrahydrofuran leads to K(t-Bu)P? ;BN(i-Pr)₂? P(t-Bu)K ( 1 ) via P? ;P bond cleavage of the three-membered ring skeleton. Above ? 78°C 1 changes into the asymmetric compound K(t-Bu)P? ;P(t-Bu)? BHN(i-Pr)₂ ( 2 ). In dimethoxyethane additionally the monometallated diphosphaborirane K(t-Bu)P₂BN(i-Pr)₂ ( 3 ) is formed. 1 and 3 , which could be isolated free from other phosphorus containing compounds, as well as the corresponding silylphosphanes Me₃Si(t-Bu)P? ;BN(i-Pr)₂? ;P(t-Bu)SiMe ₃ ( 4 ) and Me₃Si(t-Bu)P₂BN(i-Pr)₂ ( 5 ) were characterized by NMR spectroscopy. Protolysis of 3 or 5 leads to a decomposition of the three-membered ring skeleton with formation of H(t-Bu)P? ;PH₂.     

Evaluating cis‐2,6‐Dimethylpiperidide (cis‐DMP) as a Base Component in Lithium‐Mediated Zincation Chemistry

Most recent advances in metallation chemistry have centred on the bulky secondary amide 2,2,6,6‐tetramethylpiperidide (TMP) within mixed metal, often ate, compositions. However, the precursor amine TMP(H) is rather expensive so a cheaper substitute would be welcome. Thus this study was aimed towards developing cheaper non‐TMP based mixed‐metal bases and, as cis‐2,6‐dimethylpiperidide (cis‐DMP) was chosen as the alternative amide, developing cis‐DMP zincate chemistry which has received meagre attention compared to that of its methyl‐rich counterpart TMP. A new lithium diethylzincate, [(TMEDA)LiZn(cis‐DMP)Et₂] (TMEDA=N,N,N′,N′‐tetramethylethylenediamine) has been synthesised by co‐complexation of Li(cis‐DMP), Et₂Zn and TMEDA, and characterised by NMR (including DOSY) spectroscopy and X‐ray crystallography, which revealed a dinuclear contact ion pair arrangement. By using N,N‐diisopropylbenzamide as a test aromatic substrate, the deprotonative reactivity of [(TMEDA)LiZn(cis‐DMP)Et₂] has been probed and contrasted with that of the known but previously uninvestigated di‐tert‐butylzincate, [(TMEDA)LiZn(cis‐DMP)tBu₂]. The former was found to be the superior base (for example, producing the ortho‐deuteriated product in respective yields of 78 % and 48 % following D₂O quenching of zincated benzamide intermediates). An 88 % yield of 2‐iodo‐N,N‐diisopropylbenzamide was obtained on reaction of two equivalents of the diethylzincate with the benzamide followed by iodination. Comparisons are also drawn using 1,1,1,3,3,3‐hexamethyldisilazide (HMDS), diisopropylamide and TMP as the amide component in the lithium amide, Et₂Zn and TMEDA system. Under certain conditions, the cis‐DMP base system was found to give improved results in comparison to HMDS and diisopropylamide (DA), and comparable results to a TMP system. Two novel complexes isolated from reactions of the di‐tert‐butylzincate and crystallographically characterised, namely the pre‐metallation complex [{(iPr)₂N(Ph)C?O}LiZn(cis‐DMP)tBu₂] and the post‐metallation complex [(TMEDA)Li(cis‐DMP){2‐[1‐C(=O)N(iPr)₂]C₆H₄}Zn(tBu)], shed valuable light on the structures and mechanisms involved in these alkali‐metal‐mediated zincation reactions. Aspects of these reactions are also modelled by DFT calculations.     

Beiträge zur Chemie des Phosphors. 160. Zur Ringspaltung der Phosphor-Dreiringheterocyclen (t-BuP)2CMe2 und (t-BuP)2N(i-Pr) mit Kalium bzw. K-Naphthalid

Contributions to the Chemistry of Phosphorus. 160. About the Ring Cleavage of the Phosphorus Three-Membered Heterocycles (t-BuP)₂CMe₂ and (t-BuP)₂N(i-Pr) with Potassium or K-Naphthalenide The reaction of (t-BuP)₂CMe₂ with potassium or K-naphthalenide in tetrahydrofuran or 1,2-dimethoxyethane mainly leads to the symmetric phosphide K(t-Bu)P? ;CMe₂? ;P(t-Bu)K ( 1 ) via P? ;P-bond cleavage. Above —78°C 1 decomposes into the monophosphides KHP(t-Bu) ( 3 ) and KP(t-Bu)(i-Pr) ( 4 ). In the case of (t-BuP)₂N(i-Pr) under analogous conditions essentially the P? ;N-bond is split up yielding the phosphide K(t-Bu)P? ;P(t-Bu)? ;NH(i-Pr) ( 5 ), which is stable at room temperature. Contrary to (t-BuP)₂BN(i-Pr)₂ cyclic phosphides are not formed. The different reactive behavior in the metalation of phosphorus three-membered heterocycles of the type (PR¹)₂ER (E = hetero atom) is discussed.     

Ein cyclisches Arsinoschwefeldiimid als intramolekularer Brückenligand: Synthese und Röntgenstrukturanalyse von Os3(CO)10[μ-(t-Bu)As(NSN)2As(t-Bu)]

A Cyclic Arsino Sulfur Diimide as an Intramolecular Bridging Ligand: Synthesis and X-Ray Structure Analysis of Os₃(CO)₁₀[μ-(t-Bu)As(NSN)₂As(t-Bu)] The eight-membered sulfur diimide heterocycle (t-Bu)As(NSN)₂As(t-Bu) ( 8 ) can be incorporated into a trinuclear carbonylosmium cluster either as a mono- or as a bidentate ligand. Reaction of the kinetically labile acetonitrile complex Os₃(CO)₁₁(CH₃CN) with 8 in CH₂Cl₂ solution leads to a monosubstituted derivative of Os₃(CO)₁₂ of composition Os₃(CO)₁₁[(t-Bu)As(NSN)₂As(t-Bu)] ( 9 ) which still contains one uncoordinated arsenic atom; addition of a second [Os₃(CO)₁₁] fragment to 9 was not observed. However, Me₃NO-induced substitution of a carbonyl group in 9 results in coordination of the ligand 8 to the triosmium cluster through both arsenic atoms. The structure of the product Os₃(CO)₁₀[μ-(t-Bu)As(NSN)₂As(t-Bu)](10)¹ was determined by an X-ray structure analysis. I n the triangulo-triosmiumcarbonyl cluster 10 , the ligand 8 occupies two equatorial positions at two adjacent osmium atoms, being coordinated through the arsenic atoms with O s ? As distances of 2.403(1) Å The cluster molecule 10 possesses a 2-symmetry of crystallographic origin. The [Os₃(CO)₁₀] fragment and the eight-membered heterocyclic ligand are not changed significantly in their structures as compared with Os₃(CO)₁₀ and free 8 , respectively. Nevertheless, coordination of 8 imposes its lower 2-symmetry upon the [Os₃(CO)₁₀] fragment. The reduction of mm2- to 2-symmetry (C_2v to C₂) for the cyclic arsino sulfur diimide 8 is more pronounced in the complex 10 than in the free state. The As …? As distance in 10 (8.878(4) A) is considerably enlarged its compared to 8 (3.683(1) Å).     

Syntheses and X‐Ray Structures of Zinc Amidinate Complexes

Reactions of ZnX₂ (X = Cl, Br) with equimolar amounts of Li[t‐BuC(NR)₂] (R = i‐Pr, Cy) yielded mono‐amidinate complexes [{t‐BuC(NR)₂}ZnX]₂ (X = Cl, R = i‐Pr 1 , Cy 2 ; X = Br, R = i‐Pr 3 , Cy 4 ), whereas reactions with two equivalents of Li‐amidinate resulted in the formation of the corresponding bis‐amidinate complexes [t‐BuC(NR)₂]₂Zn (R = i‐Pr 5 , Cy 6 ). 1 ‐ 6 were characterized by elemental analyses, IR, mass and multinuclear NMR spectroscopy (¹H, ¹³C), and single crystal X‐ray analysis ( 1 , 2 , 3 , 6 ). In addition, the single crystal X‐ray structure of [t‐BuC(NCy)₂]ZnBr·LiBr(OEt₂)₂ 7 , which was obtained as a byproduct in low yield from re‐crystallization experiments of 4 in Et₂O, is reported.     

Kristallstruktur und Bindungsverhältnisse von [W(O-t-Bu)4(THF)]

Crystal Structure and Bonding of [W(O- t -Bu)₄(THF)] [W(O-t-Bu)₄(THF)] is formed from [WCl₄(SEt₂)₂] and LiO-t-Bu in boiling tetrahydrofuran and characterized by a crystal structure analysis. The compound crystallizes in the tetragonal space group I4 with Z = 2 and the lattice dimensions a = b = 1158.8(2) and c = 940.7(2) pm at 80 °C. [W(O-t-Bu)₄(THF)] shows the molecular structure of a tetragonal pyramid with the oxygen atom of the THF molecule in the apical position. Surprisingly, the tungsten atom is deflected by 34 pm from the plane of the four oxygen atoms of the O-t-butyl groups against the direction of the W–O(THF) bond. The bonding modes are discussed on the basis of MO considerations.     

Homoleptische Amide von Zink,Cadmium und Quecksilber

Homoleptic Amides of Zinc, Cadmium, and Mercury ZnCl₂, CdCl₂ and HgCl₂ react with the lithium salts ( 1 a–5 a ) of the sterically demanding secundary amines HN(SiMe₃)Ph ( 1 ), HN(SiMe₃)C₆H₃Me₂‐2,6 ( 2 ), HN(SiMe₃)C₆H₃ⁱPr₂‐2,6 ( 3 ), HN(SiMe₃)C₆H₃^tBu₂‐2,5 ( 4 ), and HN(SiMe₂NMe₂)C₆H₃ⁱPr₂‐2,6 ( 5 ) yielding the corresponding homoleptic metal amides Zn[N(SiMe₂R′)R]₂ ( 1 b–5 b ), Cd[N(SiMe₂R′)R]₂ ( 1 c , 5 c ), and Hg[N(SiMe₂R′)R]₂ ( 1 d–5 d ), respectively. Except the dimeric {Zn[N(SiMe₃)Ph]₂}₂ ( 1 b ), all complexes are monomeric. The compounds were characterized by elemental analyses, molecular weight determinations, NMR and mass spectra. Furthermore, the zinc amides ( 1 b–5 b ) and the mercury amides 1 d–3 d and 5 d were characterized by single crystal X‐ray structure analysis. Except 1 b and 5 b , they show a linear N–M–N arrangement.     

Beiträge zur Chemie des Phosphors. 128. Synthese des Diphosphastanna-cyclopropans (t-BuP)2Sn(t-Bu)2

Contributions to the Chemistry of Phosphorus. 128. Synthesis of the Diphosphastanna-cyclopropane (t-BuP)₂Sn(t-Bu)₂ The first three-membered P₂Sn heterocycle, 1,2,3,3-tetra-tert-butyl-1,2,3-diphosphastanna-cyclopropane (1,2,3,3-tetra-tert-butyl-1,2,3-diphosphastannirane) ( 1 ), has been synthesized by [2+1] cyclocondensation of K(t-Bu)P—P(t-Bu)K with (t-Bu)₂SnCl₂. 1 is stable at room temperature. Besides, (t-BuP)₂[Sn(t-Bu)₂]₂ ( 2 ), (t-BuP)₄Sn(t-Bu)₂ ( 3 ), and (t-BuP)₄ are formed. In the reaction with Et₂SnCl₂, the six-membered ring compound [(t-BuP)₂SnEt₂]₂ ( 4 ) is the main-product; the four- and five-membered cyclostannaphosphanes (t-BuP)₃SnEt₂ ( 5 ) and (t-BuP)₃(SnEt₂)₂ ( 6 ) are also formed. 1 could be isolated in the pure state and has been unambiguously characterized as a three-membered heterocycle with a P₂Sn skeleton. The ³¹P-NMR parameters of the other new cyclostannaphosphanes 2–6 are reported.     

Synthesis and Structures of New Oxidation/ Cycloaddition Products of λ3‐Cyclodiphosphazanes

Reaction of the cyclodiphosphazane [(OC₄H₈N)P(μ‐N‐t‐Bu)₂P(HN‐t‐Bu)] ( 1 ) with an equimolar quantity of diisopropyl azodicarboxylate afforded the phosphinimine product [(OC₄H₈N)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂ ‐i‐Pr)NHCO₂‐i‐Pr] ( 6 ) having a P^III‐N‐P^V skeleton. Similar products [(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂Et)NHCO₂Et] ( 7 ) and [(CO₂‐i‐Pr)HNN(CO₂‐i‐Pr)](t‐BuN=P(μ‐N‐t‐Bu)₂POCH₂CMe₂CH₂O[P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂‐i‐Pr)NH(CO₂‐i‐Pr)] ( 8 ) were spectroscopically characterized in the reaction of [(t‐BuNH)P‐N‐t‐Bu]₂ ( 2 ) and [(t‐BuNH)P(μ‐N‐t‐Bu)₂POCH₂CMe₂CH₂OP(μ‐N‐t‐Bu)₂P(NH‐t‐Bu)] ( 3 ) with diethyl‐ and diisopropyl azodicarboxylate, respectively. By contrast, the reaction of [(μ‐t‐BuN)P]₂[O‐6‐t‐Bu‐4‐Me‐C₆H₂]₂CH₂ ( 4 ) and [(C₅H₁₀N)P‐μ‐N‐t‐Bu]₂ ( 5 ) with diisopropyl azodicarboxylate afforded the mono‐ and bis‐oxidized compounds [(O)P(μ‐N‐t‐Bu)₂P][O‐6‐t‐Bu‐4‐Me‐C₆H₂]₂CH₂ ( 9 ) and [(C₅H₁₀N)(O)P‐μ‐N‐t‐Bu]₂ ( 10 ), respectively. Oxidative addition of o‐chloranil to 7 and its DIAD analogue [(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂‐i‐Pr)NHCO₂‐i‐Pr] ( 11 ) afforded [(C₆Cl₄‐1, 2‐O₂)(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂R)NHCO₂R] [R = Et ( 12 ) and i‐Pr ( 13 )] containing tetra‐ and pentacoordinate P^V atoms in the cyclodiphosphazane ring. The structures of 6 , 9 , 12 and 13 have been confirmed by X‐ray structure determination. For comparison, the X‐ray structure of the double cycloaddition product [(C₆Cl₄‐1, 2‐O₂)(t‐BuNH)PN‐t‐Bu]₂ ( 14 ), obtained from the reaction of 2 with two mole equivalents of o‐chloranil is also reported.     

Synthese und Kristallstrukturen der Zink-Amido-Komplexe [Zn(NPh2)2]2 und [Zn(NPh2)2(THF)2]

Synthesis and Crystal Structures of the Zinc Amido Complexes [Zn(NPh₂)₂]₂ and [Zn(NPh₂)₂(THF)₂] Zinc diphenylamide is prepared from Zn[N(SiMe₃)₂]₂ and diphenylamine by transamination reaction. The compound is characterized by a crystal structure analysis. According to it [Zn(NPh₂)₂]₂ forms centrosymmetric dimeric molecules with Zn–N distances of 185.9 pm for the terminally bonded NPh₂^– ligand and Zn–N distances of 204.0 and 202.6 pm in the four-membered ring. From tetrahydrofuran solutions [Zn(NPh₂)₂(THF)₂] crystallizes as monomeric molecular complex with Zn–N bond lengths of 192.2 pm in average.     

Towards a New Family of Photoluminescent Organozinc 8‐Hydroxyquinolinates with a High Propensity to Form Noncovalent Porous Materials

We report on investigations of reactions of tBu₂Zn with 8‐hydroxyquinoline (q‐H) and the influence of water on the composition and structure of the final product. A new synthetic approach to photoluminescent zinc complexes with quinolinate ligands was developed that allowed the isolation of a series of structurally diverse and novel alkylzinc 8‐hydroxyquinolate complexes: the trinuclear alkylzinc aggregate [tBuZn(q)]₃ ( 1₃ ), the pentanuclear oxo cluster [(tBu)₃Zn₅(μ₄‐O)(q)₅] ( 2 ), and the tetranuclear hydroxo cluster [Zn(q)₂]₂[tBuZn(OH)]₂ ( 3 ). All compounds were characterized in solution by ¹H NMR, IR, UV/Vis, and photoluminescence (PL) spectroscopy, and in the solid state by X‐ray diffraction, TGA, and PL studies. Density functional theory calculations were also carried out for these new Zn^II complexes to rationalize their luminescence behavior. A detailed analysis of the supramolecular structures of 2 and 3 shows that the unique shape of the corresponding single molecules leads to the formation of extended 3D networks with 1D open channels. Varying the stoichiometry, shape, and supramolecular structure of the resulting complexes leads to changes in their spectroscopic properties. The close‐packed crystal structure of 1₃ shows a redshifted emission maximum in comparison to the porous crystal structure of 2 and the THF‐solvated structure of 3 .     

Synthesen von Verbindungen mit M–N‐Bindungen (M = Li,Ga, In)

Syntheses of Compounds with M–N Bonds (M = Li, Ga, In) The adducts [GaCl₃(HNⁱPr₂)] ( 1 ) and [InCl₃{HN(CH₂Ph)₂}₂] ( 2 ) can be obtained by the reactions of the corresponding metal(III) halides with the amines. The In amide In(N^cHex₂)₃ ( 3 ) can be formed by treatment of InCl₃ with three equivalents of LiN^cHex₂. Reaction with four equivalents of LiN^cHex₂ leads to the same product. However, the treatment of InCl₃ with four equivalents of LiN(CH₂Ph)₂ gives the desired metalate [Li(THF)₄][In{N(CH₂Ph)₂}₄] ( 4 ). From the corresponding reaction of InCl₃ with LiNⁱPr₂ no In‐containing product could be identified. Instead, the aggregate of LiCl with three units of LiNⁱPr₂, [Li₄(NⁱPr₂)₃(THF)₄Cl] ( 5 ), was isolated. 1 – 4 were characterized by NMR, IR and MS techniques as well as by X‐ray structure determinations. According to them, 1 possesses a tetrahedrally coordinated Ga atom, at which two units of 1 are connected by hydrogen bridges to centrosymmetrical dimers. The In atoms in 2 have a trigonal‐bipyramidal coordination sphere; the amine molecules occupy the apical positions. The central metal atom in 3 and the anion of 4 exhibit trigonal‐planar and distorted tetrahedral environments, respectively. The novel structural motif in 5 is the Cl^– ion, only partly surrounded by Li⁺ ions in a strongly distorted trigonal‐bipyramidal fashion. The dominating angle amounts to 165.2(2)°.     

Zur Konkurrenz von Stickstoff- und Schwefel-Donoratomen in Zinkkomplexen: [Zn(bims)2][SiF6] · 5MeOH und [ZnCl(paps)]2(Zn2Cl6) (bims = Bis(2-benzimidazolylmethyl)sulfid; paps = o,o′-(N,N′-Dipicolinyliden)diazadiphenyldisulfid)

Competition between Nitrogen and Sulfur Donor Atoms in Zinc(II) Complexes: [Zn(bims)₂][SiF₆] · 5MeOH and [ZnCl(paps)]₂(Zn₂Cl₆) (bims = bis(2-benzimidazolylmethyl)sulfide; paps = o,o′-(N,N′-dipicolinylidene)diazadiphenyl-disulfide) [Zn(bims)₂](SiF₆) · 5 MeOH ( 1 ) was synthesized by reaction of Zn(SiF₆) with the ligand bis(2-benzimidazolylmethyl)sulfide (bims). Zinc is tetrahedrally coordinated by four benzimidazole nitrogen atoms of the two ligand molecules, the sulfur atom does not coordinate. From reaction of ZnCl₂ with o,o′-(N,N′-dipicolinylidene)diazadiphenyldisulfide (paps) [ZnCl(paps)]₂(Zn₂Cl₆) ( 2 ) was obtained. Here, an octahedral coordination by four nitrogen atoms, one sulfur atom of the ligand and one chloride ion was found. Both compounds were characterized by infrared and ¹H-NMR-spectroscopy as well as by single crystal X-ray structure analysis. Space groups and structural data: 1: P1 , a = 9.904(2), b = 10.951(3), c = 19.356(2) Å, α = 91.08(2), β = 91.11(2), γ = 95.74(2)°, R1 = 0.0631; 2: P1 , a = 9.051(3), b = 11.110(3), c = 15.170(4) Å, α = 92.99(2), β = 105.93(2), γ = 107.79(2)°, R1 = 0.0585.     

Synthesen und Strukturen von N‐Acylthioharnstoffkomplexen des Zinks und des Cadmiums

Synthesis and Structures of the Zinc‐ and Cadmium‐N‐Acylthiourea Complexes The synthesis and crystal structures of the N,N‐Diisobutyl‐N′‐benzoylthiourea complexes [Zn(Buⁱ₂btu)₂] and [Cd(Buⁱ₂btu)₂(HBuⁱ₂btu)] are reported. The complexes of Zn^II and Cd^II have different molecular structures. Whereas Zn^II forms a bischelate with tetrahedral coordination, three ligands coordinate in a trigonal‐bipyramidal manner in the Cd^II complex.     

A Comparative Study of Platinum Di (t-butyl) (15N2)diimine and trans-[(PtCl2(N-ligand)PBu3)] complexes by 195Pt-, 31P- and 15N-NMR

¹⁹⁵Pt-, ³¹P- and ¹⁵N-NMR. data are presented for [PtCl₂ (t-Bu ¹⁵N?CH? CH?¹⁵N (t-Bu)) (η²-styrene)] ( 1 ), trans-[{PtCl₂ (PBu₃)}₂ (t-Bu ¹⁵N?CH? CH?¹⁵N (t-Bu))] ( 2 ), trans-[PtCl₂ (t-Bu ¹⁵N?CH? CH?¹⁵N (t-Bu)) (PBu₃)] ( 3 ) and various complexes of the type trans-[PtCl₂ (N-ligand) (PBu₃)]. In solution the gross structural features of 1 and 2 are shown to be in agreement with those found in the solid state; namely, 1 contains five-coordinate Pt and 2 is dinuclear. In 3 Pt is four-coordinate with only one N-atom of the diimine ligand being coordinated at ?50° in CD₂Cl₂. The NMR. data for 2 and 3 are compared with those of trans-[PtCl₂ (N-ligand) (PBu₃)] (N-ligand = pyridine, 2, 6-dimethylpyridine, (¹⁵N)-hexylamine, (¹⁵N)-t-butylamine and (¹⁵N)-aniline) and are discussed in terms of the donor and acceptor properties of the N-ligands.     

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)-Centre: Labile Mono- and Bis(hydridogallyl)zinc Complexes

In the presence of TMEDA (N,N,N’,N’-tetramethylethylenediamine), partially deaggregated zinc dihydride as hydrocarbon suspensions react with the gallium(I) compound [(BDI)Ga] ( I , BDI={HC(C(CH₃)N(2,6-iPr₂-C₆H₃))₂}⁻) by formal oxidative addition of a Zn−H bond to the gallium(I) centre. Dissociation of the labile TMEDA ligand in the resulting complex [(BDI)Ga(H)−(H)Zn(tmeda)] ( 1 ) facilitates insertion of a second equiv. of I into the remaining Zn−H to form a thermally sensitive trinuclear species [{(BDI)Ga(H)}₂Zn] ( 2 ). Compound 1 exchanges with polymeric zinc dideuteride [ZnD₂]_n in the presence of TMEDA, and with compounds I and 2 via sequential and reversible ligand dissociation and gallium(I) insertion. Spectroscopic and computational studies demonstrate the reversibility of oxidative addition of each Zn−H bond to the gallium(I) centres.     

Zincocene and Dizincocene N‐Heterocyclic Carbene Complexes and Catalytic Hydrogenation of Imines and Ketones

The N‐heterocyclic carbene (NHC) adducts Zn(Cp^R)₂(NHC)] (Cp^R=C₅HMe₄, C₅H₄SiMe₃; NHC=ItBu, IDipp (Dipp=2,6‐diisopropylphenyl), IMes (Mes=mesityl), SIMes) were prepared and shown to be active catalysts for the hydrogenation of imines, whereas decamethylzincocene [ZnCp*₂] is highly active for the hydrogenation of ketones in the presence of noncoordinating NHCs. The abnormal carbene complex [Zn(OCHPh₂)₂(aItBu)]₂ was formed from spontaneous rearrangement of the ItBu ligand during incomplete hydrogenation of benzophenone. Two isolated Zn^I adducts [Zn₂Cp*₂(NHC)] (NHC=ItBu, SIMes) are presented and characterized as weak adducts on the basis of ¹³C NMR spectroscopic and X‐ray diffraction experiments. A mechanistic proposal for the reduction of [ZnCp*₂] with H₂ to give [Zn₂Cp*₂] is discussed.     

Beiträge zur Chemie des Phosphors. Synthese und Eigenschaften des 1,2-Diphospha-3,4-diboretans (t-BuP)2(BNMe2)2

Contributions tot he Chemistry of Phosphorus. 148. Synthesis and Properties of the 1,2-Diphospha-3,4-diboretane (t-BuP)₂(BNMe₂)₂ The first 1, 2-diphospha-3,4-diboretane (1,2-diphospha-3, 4-diboracyclobutane) (t-BuP)₂(BNMe₂)(1) was prepared by [2+2] cyclocondensation of K(t-Bu)P? P(t-Bu)K with Cl(Me₂N)B? B(NMe₂)Cl. 1 could be isolated in the pure state and was NMR spectroscopically characterized as a compound with a planar P₂ B₂ ring skeleton.     

Highly Active,Low‐Valence Molybdenum‐ and Tungsten‐Amide Catalysts for Bifunctional Imine‐Hydrogenation Reactions

The reactions of [M(NO)(CO)₄(ClAlCl₃)] (M=Mo, W) with (iPr₂PCH₂CH₂)₂NH, (PN^HP) at 90 °C afforded [M(NO)(CO)(PN^HP)Cl] complexes (M=Mo, 1a ; W, 1b ). The treatment of compound 1a with KOtBu as a base at room temperature yielded the alkoxide complex [Mo(NO)(CO)(PN^HP)(OtBu)] ( 2a ). In contrast, with the amide base Na[N(SiMe₃)₂], the PN^HP ligand moieties in compounds 1a and 1b could be deprotonated at room temperature, thereby inducing dehydrochlorination into amido complexes [M(NO)(CO)(PNP)] (M=Mo, 3a ; W, 3b ; PNP=(iPr₂PCH₂CH₂)₂N)). Compounds 3a and 3b have pseudo‐trigonal‐bipyramidal geometries, in which the amido nitrogen atom is in the equatorial plane. At room temperature, compounds 3a and 3b were capable of adding dihydrogen, with heterolytic splitting, thereby forming pairs of isomeric amine‐hydride complexes [Mo(NO)(CO)H(PN^HP)] ( 4a(cis) and 4a(trans) ) and [W(NO)(CO)H(PN^HP)] ( 4b(cis) and 4b(trans) ; cis and trans correspond to the position of the H and NO groups). H₂ approaches the Mo/W?N bond in compounds 3a , 3b from either the CO‐ligand side or from the NO‐ligand side. Compounds 4a(cis) and 4a(trans) were only found to be stable under a H₂ atmosphere and could not be isolated. At 140 °C and 60 bar H₂, compounds 3a and 3b catalyzed the hydrogenation of imines, thereby showing maximum turnover frequencies (TOFs) of 2912 and 1120 h^?1, respectively, for the hydrogenation of N‐(4 ‐ methoxybenzylidene)aniline. A Hammett plot for various para‐substituted imines revealed linear correlations with a negative slope of ?3.69 for para substitution on the benzylidene side and a positive slope of 0.68 for para substitution on the aniline side. Kinetics analysis revealed the initial rate of the hydrogenation reactions to be first order in c(cat.) and zeroth order in c(imine). Deuterium kinetic isotope effect (DKIE) experiments furnished a low k_H/k_D value (1.28), which supported a Noyori‐type metal–ligand bifunctional mechanism with H₂ addition as the rate‐limiting step.