Synthesis and molecular structure of Cr(salen)(μ‐N)RhCl(COD): the first example of a heterobimetallic nitride‐bridged complex containing chromium

Five‐coordinate Cr(N)(salen) {salen is 2,2′‐[ethane‐1,2‐diylbis(nitrilomethylidyne)]diphenolate} reacts with [RhCl(COD)]₂ (COD is 1,5‐cyclooctadiene) to yield the heterobimetallic nitride‐bridged title compound, namely chlorido‐2κCl‐[2(η⁴)‐1,5‐cyclooctadiene]{2,2′‐[ethane‐1,2‐diylbis(nitrilomethylidyne)]diphenolato‐1κ⁴O,N,N′,O′}‐μ‐nitrido‐1:2κ²N:N‐chromium(V)rhodium(I), [CrRh(C₁₆H₁₄N₂O₂)ClN(C₈H₁₂)]. The Cr—N bond of 1.5936 (14) Å is elongated by only 0.035 Å compared to the terminal Cr—N bond in the precursor. The nitride bridge is close to being linear [173.03 (9)°] and the Rh—N bond of 1.9594 (14) Å is very short for a monodentate nitrogen‐donor ligand, indicating significant π‐acceptor character of the Cr[triple‐bond]N group.     

Versatile reactivity of half-sandwich Ir and Rh complexes toward carboranylamidinates and their derivatives: synthesis, structure, and catalytic activity for norbornene polymerization

Synthesis, structure, and reactivity of carboranylamidinate‐based half‐sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ‐Cl)Cl}₂] (M=Ir, Rh; Cp*=η⁵‐C₅Me₅) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18‐electron complexes [Cp*IrCl(Cab^N‐DIC)] ( 1 a ; Cab^N‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHiPr)]), [Cp*RhCl(Cab^N‐DIC)] ( 1 b ), and [Cp*RhCl(Cab^N‐DCC)] ( 1 c ; Cab^N‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHCy)]). A series of 16‐electron half‐sandwich Ir and Rh complexes [Cp*Ir(Cab^N′‐DIC)] ( 2 a ; Cab^N′‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NiPr)]), [Cp*Ir(Cab^N′‐DCC)] ( 2 b , Cab^N′‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NCy)]), and [Cp*Rh(Cab^N′‐DIC)] ( 2 c ) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab^N,S‐DIC)], [Cp*M(Cab^N,S‐DCC)] (M=Ir 3 a , 3 b ; Rh 3 c , 3 d ), formed through BH activation, are obtained by reaction of [{Cp*MCl₂}₂] with carboranylamidinate sulfides [RN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHR)]S^? (R=iPr, Cy), which can be prepared by inserting sulfur into the C? Li bond of lithium carboranylamidinates. Iridium complex 1 a shows catalytic activities of up to 2.69×10⁶ g_PNB ${{\rm{mol}}_{{\rm{Ir}}}^{ - {\rm{1}}} }Synthesis, structure, and reactivity of carboranylamidinate-based half-sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ-Cl)Cl}(2)] (M = Ir, Rh; Cp* = η(5)-C(5)Me(5)) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18-electron complexes [Cp*IrCl(Cab(N)-DIC)] (1?a; Cab(N)-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NHiPr)]), [Cp*RhCl(Cab(N)-DIC)] (1?b), and [Cp*RhCl(Cab(N)-DCC)] (1?c; Cab(N)-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10))(NHCy)]). A series of 16-electron half-sandwich Ir and Rh complexes [Cp*Ir(Cab(N')-DIC)] (2?a; Cab(N')-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NiPr)]), [Cp*Ir(Cab(N')-DCC)] (2?b, Cab(N')-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10)(NCy)]), and [Cp*Rh(Cab(N')-DIC)] (2?c) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab(N,S)-DIC)], [Cp*M(Cab(N,S)-DCC)] (M = Ir 3?a, 3?b; Rh 3?c, 3?d), formed through BH activation, are obtained by reaction of [{Cp*MCl(2)}(2)] with carboranylamidinate sulfides [RN=C(closo-1,2-C(2)B(10)H(10))(NHR)]S(-) (R = iPr, Cy), which can be prepared by inserting sulfur into the C-Li bond of lithium carboranylamidinates. Iridium complex 1?a shows catalytic activities of up to 2.69×10(6) g(PNB) mol(Ir)(-1) h(-1) for the polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. Catalytic activities and the molecular weight of polynorbornene (PNB) were investigated under various reaction conditions. All complexes were fully characterized by elemental analysis and IR and NMR spectroscopy; the structures of 1?a-c, 2?a, b; and 3?a, b, d were further confirmed by single crystal X-ray diffraction.     

Synthesis,characterization and crystal structures of the bidentate Schiff base N,N′‐bis(2‐nitrocinnamaldehyde)ethylenediamine and its complex with CuNCS and triphenylphosphane

Reaction of copper(I) thiocyanate and triphenylphosphane with the bidentate Schiff base N,N′‐bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine {Nca₂en, (1); systematic name (1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]}, C₂₀H₁₈N₄O₄, in a 1:1:1 molar ratio in acetonitrile resulted in the formation of the complex {(1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]‐κ²N,N′}(thiocyanato‐κN)(triphenylphosphane‐κP)copper(I)], [Cu(NCS)(C₂₀H₁₈N₄O₄)(C₁₈H₁₅P)] or [Cu(NCS)(Nca₂en)(PPh₃)], (2). The Schiff base and copper(I) complex have been characterized by elemental analyses, IR, electronic and ¹H NMR spectroscopy, and X‐ray crystallography [from synchrotron data for (1)]. The molecule of (1) lies on a crystallographic inversion centre, with a trans conformation for the ethylenediamine unit, and displays significant twists from coplanarity of its nitro group, aromatic ring, conjugated chain and especially ethylenediamine segments. It acts as a bidentate ligand coordinating via the imine N atoms to the Cu^I atom in complex (2), in which the ethylenediamine unit necessarily adopts a somewhat flattened gauche conformation, resulting in a rather bowed shape overall for the ligand. The NCS⁻ ligand is coordinated through its N atom. The geometry around the Cu^I atom is distorted tetrahedral, with a small N—Cu—N bite angle of 81.56 (12)° and an enlarged opposite angle of 117.29 (9)° for SCN—Cu—P. Comparisons are made with the analogous Schiff base having no nitro substituents and with metal complexes of both ligands.     

3‐Rhoda‐1,2‐diazacyclopentanes: A Series of Novel Metallacycle Complexes Derived From CN Functionalization of Ethylene

Rh‐containing metallacycles, [(TPA)Rh^III(κ²‐(C,N)‐CH₂CH₂(NR)₂‐]Cl; TPA=N,N,N,N‐tris(2‐pyridylmethyl)amine have been accessed through treatment of the Rh^I ethylene complex, [(TPA)Rh(η²‐CH₂CH₂)]Cl ([ 1 ]Cl) with substituted diazenes. We show this methodology to be tolerant of electron‐deficient azo compounds including azo diesters (RCO₂N?NCO₂R; R=Et [ 3 ]Cl, R=iPr [ 4 ]Cl, R=tBu [ 5 ]Cl, and R=Bn [ 6 ]Cl) and a cyclic azo diamide: 4‐phenyl‐1,2,4‐triazole‐3,5‐dione (PTAD), [ 7 ]Cl. The latter complex features two ortho‐fused ring systems and constitutes the first 3‐rhoda‐1,2‐diazabicyclo[3.3.0]octane. Preliminary evidence suggests that these complexes result from N–N coordination followed by insertion of ethylene into a [Rh]?N bond. In terms of reactivity, [ 3 ]Cl and [ 4 ]Cl successfully undergo ring‐opening using p‐toluenesulfonic acid, affording the Rh chlorides, [(TPA)Rh^III(Cl)(κ¹‐(C)‐CH₂CH₂(NCO₂R)(NHCO₂R)]OTs; [ 13 ]OTs and [ 14 ]OTs. Deprotection of [ 5 ]Cl using trifluoroacetic acid was also found to give an ethyl substituted, end‐on coordinated diazene [(TPA)Rh^III(κ²‐(C,N)‐CH₂CH₂(NH)₂‐]⁺ [ 16 ]Cl, a hitherto unreported motif. Treatment of [ 16 ]Cl with acetyl chloride resulted in the bisacetylated adduct [(TPA)Rh^III(κ²‐(C,N)‐CH₂CH₂(NAc)₂‐]⁺, [ 17 ]Cl. Treatment of [ 1 ]Cl with AcN?NAc did not give the Rh?N insertion product, but instead the N,O‐chelated complex [(TPA)Rh^I ( κ²‐(O,N)‐CH₃(CO)(NH)(N?C(CH₃)(OCH?CH₂))]Cl [ 23 ]Cl, presumably through insertion of ethylene into a [Rh]?O bond.     

Synthesis and structural investigations of rhodium(I) complexes withN-phenylanthranilic acid

Summary The carbonyl-N-phenylanthranilatorhodium(I) complex [Rh(CO)₂(FA)] (1) was obtained by heating RhCl₃ · 3 H₂O withN-phenylanthranilic acid (HFA) in boiling dimethylformamide (DMF). Triphenylphosphine, PPh₃, can replace one carbonyl ligand in complex (1) to produce [Rh(CO)(PPh₃)(FA)] (2). Complexes (1) and (2) were characterized by analytical and physicochemical methods.     

Generation and Reactivity of {(Ethane‐1,2‐diyl)bis[diisopropylphosphine‐κP]}‐{[2,4,6‐tri(tert‐butyl)phenyl]phosphino‐κP}rhodium ([Rh{PH(tBu3C6H2)}(iPr2PCH2CH2PiPr2)]): Catalytic C−P Bond Formation via Intramolecular C−H/P−H Dehydrogenative Cross‐Coupling

The complex [Rh(η³‐benzyl)(dippe)] ( 1 ; dippe=bis(diisopropylphosphino)ethane=(ethane‐1,2‐diyl)bis[diisopropylphosphine]) reacted cleanly with Mes*PH₂ ( 2 ; Mes*=2,4,6‐^tBu₃C₆H₂) to provide a new Rh species [Rh(H)(dippe)(L)] ( 3 ), L being the 2,3‐dihydro‐3,3‐dimethyl‐1H‐phosphindole ligand 4 (=^tBu₂C₆H₂(CMe₂CH₂PH)) (Scheme 1). Complex 3 was converted to the corresponding chloride [Rh(Cl)(dippe)(L)] ( 6 ) when treated with CH₂Cl₂, whereas the dimeric species [Rh₂{μ‐^tBu₂C₆H₂(CMe₂CH₂P)}(μ‐H)(dippe)₂] ( 7 ) was formed upon thermolysis in toluene (Scheme 2). The structures of 6 and 7 ⋅C₇H₈ were determined by X‐ray crystallography. Complexes 1 and 3 served as catalyst precursors for the dehydrogenative coupling of C−H and P−H bonds in the conversion of 2 to 4 (Scheme 3). Deuteration studies with Mes*PD₂ exposed a complex series of bond‐activation pathways that appear to involve C−H activation of the dippe ligand by the Rh‐atom (Schemes 4 and 5)     

Systematische Studie zu den Koordinationseigenschaften des Guanidin‐Liganden Bis(tetramethylguanidino)propan mit den Metallen Mangan,Cobalt, Nickel,Zink, Cadmium,Quecksilber und Silber

The transition metal complexes with the ligand 1,3‐bis(N,N,N′,N′‐tetramethylguanidino)propane (btmgp), [Mn(btmgp)Br₂] ( 1 ), [Co(btmgp)Cl₂] ( 2 ), [Ni(btmgp)I₂] ( 3 ), [Zn(btmgp)Cl₂] ( 4 ), [Zn(btmgp)(O₂CCH₃)₂] ( 5 ), [Cd(btmgp)Cl₂] ( 6 ), [Hg(btmgp)Cl₂] ( 7 ) and [Ag₂(btmgp)₂][ClO₄]₂·2MeCN ( 8 ), were prepared and characterised for the first time. The stoichiometric reaction of the corresponding water‐free metal salts with the ligand btmgp in dry MeCN or THF resulted in the straightforward formation of the mononuclear complexes 1 – 7 and the binuclear complex 8 . In complexes with M^II the metal ion shows a distorted tetrahedral coordination whereas in 8 , the coordination of the M^I ion is almost linear. The coordination behavior of btmgp and resulting structural parameters of the corresponding complexes were discussed in an comparative approach together with already described complexes of btmgp and the bisguanidine ligand N¹,N²‐bis(1,3‐dimethylimidazolidin‐2‐ylidene)‐ethane‐1,2‐diamine (DMEG₂e), respectively.     

Diferrocenylmercury‐Bridged Diphosphine: A Chiral,Ambiphilic, and Redox‐Active Bidentate Ligand

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox‐active and ambiphilic character is reported. Initially generated as its HgCl₂ complex by reaction of 1,2‐fc(PPh₂)(SnMe₃) (fc=ferrocenediyl) with HgCl₂ in acetone, treatment with [n‐Bu₄N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg?Cl→Hgfc₂ (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh₂)₂?HgCl₂ where the bridging mercury atom acts as a σ‐acceptor. Furthermore, a bis‐[Rh(COD)Cl] complex is introduced, which displays relatively short Rh???Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh???Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10^?2 and 1.4×10^?2 e/a₀³ at the bond critical points.     

Synthesis and reactivity of rhodium(I) complexes of the type Rh(L-L)(CO)[P(OPh)3] and Rh(L-L)[P(OPh)3]2

Summary The carbonyl ligands in the Rh¹ complexes Rh(L-L)(CO)₂ [L-L=anthranilate (AA) orN-phenylanthranilate(FA) ions] are replaced by P(OPh)₃ to form the mono-or disubstituted products, Rh(L-L)(CO)[P(OPh)₃] and Rh(L-L)[P(OPh)₃]₂ respectively depending on the [P(OPh)₃]/[Rh] molar ratio, at room temperature and in air. Under argon at [P(OPh)₃]/[Rh]4 theortho-metallated Rh¹ complex Rh[P(OPh)₃]₃[P(OC₆H₄)-OPh)₂] is formed. The new route forortho-metallated Rh¹ complex synthesis is described.The Rh(AA)(CO)₂ complex was used as a catalyst precursor in hydroformylation of olefins.     

Complexes of Rhodium(III) with Two Chelating C⁁N Ligands and One Diimine Ligand

The synthesis of two series of cyclometalated Rh^III compounds is described, namely of 5 dinuclear chlorobridged species [{Rh(C?N)₂} (μ-Cl)₂] A and of 15 mononuclear complexes [Rh(C?N)₂(N?N)]⁺ B ; C?N stands for five different cyclometalating ligands, i.e. deprotonated phenylpyridine, deprotonated 2-(thienyl)pyridine, and three deprotonated 1-aryl-1H-pyrazoles, and N?N for six diimine ligands such as 2,2-bihyridine, 2,2′-bi-1H-imidazole, and 2,2′-bipyrimidine. For (2,2′-bipyridine)bis[2-(thien-2-yl)pyridinato-N,C^3′]rhodium(III) chloride, an X-ray structure determination was carried out. In the other cases, ¹H-NMR spectra established the configuration of the complexes. All mononuclear and dinuclear complexes show a C,C cis-configuration. The UV/VIS-absorption bands at longest wavelength are most likely due to metal-to-ligand charge-transfer (MLCT) transitions, depending on the nature of the cyclometalating ligand C?N and on the diimine ligand N?N. The receptor orbital is in some cases on the cyclometalating ligand, in others on the diimine. All monomer complexes exhibit at least one reversible reduction wave in the cyclovoltammogram in dimethylformamide solutions, attributable to a ligand-centered reduction. It is, therefore, concluded that the LUMO in [Rh(C?N)₂(N?N)]⁺ is of L(π*) character, as opposed to [Rh(bpy)₃]³⁺, where it is a metal d-orbital. The crystal system of (2,2′-bipyridine)bis[2-(thien-2-yl)pyridinato-N,C_3′]rhodium(III) chloride—water (1/2.125) is tetragonal (space group P⁴; R = 0.036, R_w = 0.040). The Rh-atom has slightly distorted octahedral environment; the average distances are (Rh? N/thienyl? pyridine) = 2.060 (3), Rh? C = 1.9885 (3), and Rh? N(bipyridine) = 2.1415 (3) Å. Of the three ligands the 2,2′-bipyridine is the most planar.     

Synthesis of a rhodium(I) carbonyl complex with a chiral aminodiphosphine ligand and its immobilization onto aminopropyl functionalized silica gel

The reaction of [Rh(CO)₂(µ-Cl)]₂ with two molar equivalents of a chiral ligand, (R)-N,N-bis(2-diphenylphosphinoethyl)-1-phenylethylamine(PNP*) yield a mono-carbonyl complex, [Rh(CO)Cl(η²-P,P-PNP*)] (1), in which the potentially tridentate PNP* ligand coordinates in a bidentate fashion through P,P bonding. The complex was characterized by elemental analysis, FAB mass, IR, UV-Vis, ¹H- and ³¹P{¹H}-NMR spectroscopy. Variable temperature (223–298 K) ³¹P{¹H}-,NMR spectra of 1 showed a mixture of cis and trans isomers in the solution with the trans predominating at room temperature and the cis at lower temperature. Complex 1 was immobilized on silica through axial coordination of amine from 3-aminopropyltriethoxysilane functionalized silica. The immobilized materials were characterized by elemental analysis (N₂), FTIR, DTA–TGA, N₂-adsorption, XRD, and SEM analysis.     

A Metal‐Containing N‐Heterocyclic Germylene Based on an Oxalamidine Framework

A metal‐containing N‐heterocyclic germylene based on a N‐mesityl (Mes)‐substituted oxalamidine framework is reported. The precursor (MesN=)₂C–C(–N(H)Mes)₂ ( 1 H₂) was converted into its rhodium complex [Rh(κ²N‐ 1 H₂)(cod)][OTf] ( 2 ) (cod = 1,5‐cyclooctadiene; OTf = triflate) in 62 % isolated yield. Subsequent reaction of 2 with Ge{N(SiMe₃)₂}₂ gave the crystalline N‐heterocyclic germylene [Rh(cod)(μ‐ 1 )Ge][OTf] ( 3 ) in 50 % yield. The compounds under study were fully characterized by various methods, also including X‐ray crystallographic studies on single crystals of 2 and 3 . Density functional theory (DFT) calculations revealed that π conjugation in the bridging oxalamidine framework is increased and n(N)–p(Ge) π bonding is decreased upon κ²N metal coordination; a further weakening of the Ge–N bond occurs through triflate coordination to the Ge^II atom. Nevertheless, preliminary coordination studies revealed that 3 behaves as 2‐electron (L ‐type) germylene donor ligand. Treatment of 3 with [Ir(cod)Cl]₂ furnished the heterobimetallic complex [Rh(cod)(μ‐ 1 )Ge‐Ir(cod)Cl][OTf] ( 4 ), as evidenced by NMR spectroscopic investigations and DFT calculations.     

Diferrocenylmercury‐Bridged Diphosphine: A Chiral,Ambiphilic, and Redox‐Active Bidentate Ligand

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox‐active and ambiphilic character is reported. Initially generated as its HgCl₂ complex by reaction of 1,2‐fc(PPh₂)(SnMe₃) (fc=ferrocenediyl) with HgCl₂ in acetone, treatment with [n‐Bu₄N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg−Cl→Hgfc₂ (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh₂)₂⋅HgCl₂ where the bridging mercury atom acts as a σ‐acceptor. Furthermore, a bis‐[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10⁻² and 1.4×10⁻² e/a₀³ at the bond critical points.     

Synthesis and reactivity of formamidinato rhodium(I) complexes

The syntheses of [Rh(diol)(formamidine)]₂ complexes (diol  cycloocta-1,5-diene (1); diol  norbornadiene (2); formamidine  N,N′-di-p-tolylformamidine) are reported. These complexes are dimeric and contain the bridging formamidino ligand. They react with CO, dppe and PPh₃ with displacement of the diene ligand to yield the known [Rh(CO)₂(formamidine)]₂, [Rh(dppe)₂]⁺ and [Rh(PPh₃)₂(formamidine)], respectively; the last complex, in which the formamidine acts as a chelating ligand, was isolated only as the O₂ adduct. With HCl or HBF₄ aqueous 1 and 2 do not form hydrides but instead the formamidino cation [p-tolyl-NHCHNHtolyl-p]⁺ and the complexes [Rh(diol)X]₂ (X  Cl, F); a possible scheme for the reaction with HCl is proposed. The [Rh(C₈H₁₂)(formamidine)]₂ complex reacts with heterocumulenes as CS₂, SO₂, PhNCS and PhNCO with diene displacement; the only product isolated was [Rh(CS₂)₂(formamidine], to which a polymeric structure is assigned.     

The mononuclear cobalt(II) complex CoII(DMBDIZ)2(NCS)2, where DMBDIZ is 2,6‐di­methyl­benzo[1,2‐d:4,5‐d′]­di­imidazole

In the title mononuclear cobalt complex, bis(2,6‐di­methyl‐1H,7H‐benzo­[1,2‐d:4,5‐d′]­di­imidazole‐κN³)­bis­(thio­cyanato‐κN)cobalt(II), [Co^II(NCS)₂(DMBDIZ)₂] or [Co(NCS)₂(C₁₀H₁₀N₄)₂], the cobalt(II) ion is coordinated to four N atoms, from two thio­cyanate anions and two DMBDIZ ligands, in a distorted tetrahedral geometry. In the DMBDIZ ligand, the two imine N atoms are positioned cis with respect to one another. The crystal packing of the complex is dominated by both hydrogen bonding, involving two N—H?N and two N—H?S interactions, and aromatic π–π stacking.     

Calcium Hydride Catalyzed Highly 1,2‐Selective Pyridine Hydrosilylation

Reaction of the calcium hydride complex (DIPPnacnac‐CaH?THF)₂ with pyridine is much faster and selective than that of the corresponding magnesium hydride complex (DIPPnacnac = [(2,6‐iPr₂C₆H₃)NC(Me)]₂CH). With a range of pyridine, picoline and quinoline substrates, exclusive transfer of the hydride ligand to the 2‐position is observed and also at higher temperatures no 1,2→1,4 isomerization is found. The heteroleptic product DIPPnacnac‐Ca(1,2‐dihydropyridide)?(pyridine) shows fast ligand exchange into homoleptic calcium complexes and therefore could not be isolated. Calcium hydride reduction of isoquinoline gave well‐defined homoleptic products which could be characterized by X‐ray diffraction: Ca(1,2‐dihydroisoquinolide)₂?(isoquinoline)₄ and Ca₃(1,2‐dihydroisoquinolide)₆?(isoquinoline)₆. The striking selectivity difference in the dearomatization of pyridines by Mg or Ca complexes could be explained by DFT theory and was utilized in catalysis. Whereas hydroboration of pyridine with pinacol borane with a calcium hydride catalyst gave only minor conversion, the hydrosilylation of pyridine and quinolines with PhSiH₃ yields exclusively 1,2‐dihydropyridine and 1,2‐dihydroquinoline silanes with 80–90 % conversion. Similar results can be achieved with the catalyst Ca[N(SiMe₃)₂]₂?(THF)₂. These calcium complexes represent the first catalysts for the 1,2‐selective hydrosilylation of pyridines.     

Selective and Efficient Cycloisomerization of Alkynols Catalyzed by a New Ruthenium Complex with a Tetradentate Nitrogen–Phosphorus Mixed Ligand

The new ruthenium complex [Ru(N₃P)(OAc)][BPh₄] ( 4 ), in which N₃P is the N,P mixed tetradentate ligand N,N‐bis[(pyridin‐2‐yl)methyl]‐[2‐(diphenylphosphino)phenyl]methanamine was synthesized. The complex was found to be catalytically active for the endo cycloisomerization of alkynols. The catalytic reactions can be used to synthesize five‐, six‐, and seven‐membered endo‐cyclic enol ethers in good to excellent yields. A catalytic cycle involving a vinylidene intermediate was proposed for the catalytic reactions. Treatment of complex 4 with PhC?CH and H₂O gave the alkyl complex [Ru(CH₂Ph)(CO)(N₃P)][BPh₄] ( 30 ), which supports the assumption that the catalytic reactions involve addition of a hydroxyl group to the C?C bond of vinylidene ligands.     

The formation of 'classical' and 'half unit' Schiff-base ligands from their components on a molybdenum(IV) centre

The in situ synthesis of the complex, (PPh₄)[Mo(CN)₃O(aceen)] (aceen = N-[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine), with a 'half unit' Schiff base ligand (with a free amino group) is described and compared with that of [Mo(CN)₂O(diaceen)]·H₂O (diaceen = N,N-bis[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine) in which a 'classical', tetradentate Schiff base ligand is formed. The mechanism of the 'half unit' and 'classical' template Schiff bases ligand formation is discussed.     

Magnetic Ordering in Iron(II) Complexes due to a 2D Network of Hydrogen Bonds

The magnetic properties of two octahedral iron(II) complexes with Schiff base like equatorial N₂O₂ coordinating ligands and methanol (MeOH) as axial ligand are reported. Both compounds [FeL1(MeOH)₂] ( 1 ) and [FeL2(MeOH)₂] ( 2 ) (with L1 = [3,3′]‐[1,2‐phenylenebis(iminomethylidyne)‐bis(2,4‐pentanedionato)(2‐)‐N,N′,O²,O²′] and L2 = [E,E]‐[{diethyl 2,2′‐1,2‐phenylenebis(iminomethylidyne)bis(3‐oxo‐3‐phenylpropanato)} (2‐)‐N,N′,O3,O3′]) show a weak spontaneous magnetization below T_C = 10 K. Results from X‐ray structure analysis of 1 indicate, that this is due to 2D network of hydrogen bonds as previously discussed for a similar complex.     

An Isolated Nitridyl Radical‐Bridged {Rh(N.)Rh} Complex

Photochemical activation of [(PNNH)Rh(N₃)] (PNNH=6‐di‐(tert‐butyl)phosphinomethyl‐2,2′‐bipyridine) complex 2 produced the paramagnetic (S=1/2), [(PNN)Rh?N^.‐Rh(PNN)] complex 3 (PNN^?=methylene‐deprotonated PNNH), which could be crystallographically characterized. Spectroscopic investigation of 3 indicates a predominant nitridyl radical (^.N^2?) character, which was confirmed computationally. Complex 3 reacts selectively with CO, producing two equivalents of [(PNN)Rh^I(CO)] complex 4 , presumably by nitridyl radical N,N‐coupling.