Formamidinate Ligands Research Articles

Iron‐Catalyzed Epoxidation of Aromatic Olefins and 1,3‐Dienes

AbstractThe combination of iron(III) chloride, pyridine‐2,6‐dicarboxylic acid and formamidine ligands allows for the epoxidation of styrenes and conjugated dienes in excellent chemoselectivity and yields.

The synthesis and characterization of aluminum, gallium and zinc formamidinates

Reactions of the formamidinate ligand, RN(H)C(H)NR, L H, (R = 2,6-diisopropylphenyl), with AlMe 3, AlMe 2Cl, GaMe 3 and ZnEt 2 were investigated to examine potential coordination modes of the ligand and the effect of hydrolysis on the products. Nine new complexes have been fully characterized by X-ray crystallography and other spectroscopic techniques and highlight the diverse coordination modes of the formamidinate ligand.

Guanidinate derivatives of rare-earth metals. The synthesis, properties, and molecular structures of the complexes {(Me3Si)2NC(NPri)2}3Nd, {(Me3Si)2NC(NCy)2}3Lu, and {(Me3Si)2NC(NPri)2}2HC(NPri)2}Nd

The reactions of anhydrous LnCl3 (Ln = Nd or Lu) with three equivalents of {(Me3Si)2NC(NR)2}Li (R = Pri or Cy; Cy is cyclohexyl) in THF afforded the corresponding tris(guanidinate) derivatives of lanthanides {(Me3Si)2NC(NR)2}3Ln (Ln = Nd, R = Pri, (1); Ln = Lu, R = Cy (2)), which were isolated after the recrystallization from hexane in 82 and 88% yields, respectively. The complex {(Me3Si)2NC(NCy)2}2{HC(NCy)2}Nd (3) containing two guanidinate ligands and one formamidinate ligand was isolated in attempting to synthesize the bis(guanidinate) borohydride derivative by the reaction of {(Me3Si)2NC(N-Cy)2}Na with Nd(BH4)3(THF)2 (in a molar ratio of 2: 1) in THF. This complex is apparently formed as a result of the fragmentation and redistribution of the guanidinate ligands. The X-ray diffraction study showed that in the crystalline state compounds 1–3 are mononuclear complexes containing no coordinated Lewis bases.

A Tetragonal and an Uncommon Trigonal Dicobalt Paddlewheel Compound

Two dicobalt compounds containing Co–Co bonds with DAniF ligands (DAniF = N,N′-di-p-anisylformamidinate) were synthesized and characterized by X-ray crystallography. One has a typical tetragonal paddlewheel structure, Co2(DAniF)4 (1), while the other one has a rare trigonal paddlewheel structure with three formamidinate ligands spanning a low oxidation state in the Co 2 3+ unit in Co2(DAniF)3 (2). The singly bonded Co–Co distance in the Co 2 4+ unit in 1 is 2.3580(16) A while the Co–Co bond distance in 2 is 2.3773(5) A. The average torsion angles are 10.46° and 2.34° for 1 and 2, respectively. Compound 1 is diamagnetic but 2 is paramagnetic as shown by the 1H NMR spectra.

Precursors for Assembly of Supramolecules Containing Quadruply Bonded Cr24+ Units: Systematic Preparation of Cr2(formamidinate)n(acetate)4–n (n = 2–4)

AbstractFour quadruply bonded dichromium complexes with mixed‐ligand sets, Cr2(formamidinate)n(acetate)4–n (n = 2–4), were synthesized from reactions of anhydrous Cr2(O2CCH3)4 and formamidinate anions. The Cr–Cr bond lengths fall in the range for “supershort” Cr–Cr bonds as they vary from 1.8897(5) Å to 2.012(1) Å. The distance variation depends on the presence or absence of weak axial interactions. Because formamidinate ligands are less labile than acetate groups, these compounds may be useful building blocks for the construction of neutral supramolecules having dichromium units linked by polydentate dianions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Dimolybdenum complexes containing anions of N, N′-bis(pyrimidine-2-yl)formamidine and N-(2-pyrimidinyl)formamide

The reactions of Mo 2(O 2CCH 3) 4 with different equivalents of N, N′-bis(pyrimidine-2-yl)formamidine (H L1) and N-(2-pyrimidinyl)formamide (H L2) afforded dimolybdenum complexes of the types Mo 2(O 2CCH 3)( L1) 2( L2) ( 1) trans-Mo 2( L1) 2( L2) 2 ( 2) cis-Mo 2( L1) 2( L2) 2 ( 3) and Mo 2( L2) 4 ( 4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1– 3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1– 4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo⋯N and Mo⋯O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo⋯O interactions.

Crystal structures and solution behaviors of dinuclear d10-metal complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine

The salts of Zn(II), Cd(ii) and Hg(II) react instantaneously with Kpmf (pmf(-) = anion of N,N'-bis(pyrimidine-2-yl)formamidine, Hpmf) in THF, producing bimetallic complexes of the types [M(2)(pmf)(3)](X) (M = Zn(II), X = I(3)(-), ; M = Zn(II), X = NO(3)(-), ; M = Zn(II), X = ClO(4)(-), ; M = Cd(II), X = NO(3)(-), ; M = Cd(II), X = ClO(4)(-), ) and Hg(2)(pmf)(2)X(2) (X = Cl, ; Br, ; I, ). New tridentate and tetradentate coordination modes were observed for the pmf(-) ligands and their fluxional behaviors investigated by measuring variable-temperature (1)H NMR spectra. Complexes and , which possess only tetradentate coordination modes for the pmf(-) ligands in the solid state show larger free energy of activation (DeltaG(c)( not equal)) for the exchange than complexes and with tetradentate and/or tridentate coordination modes. Complexes and are the first dinuclear Zn(II) and Hg(II) complexes containing formamidinate ligands. Moreover, the separation between the two Hg(II) atoms are 3.4689(9), 3.4933(13) and 3.5320(10) A for complexes , respectively, similar to the sum of van der Waals radii of two Hg(II) atoms which is 3.50(7) A. All the complexes exhibit emissions and the nature of the anions hardly change the emission wavelengths of the complexes with the same metal centers. The emission bands may be tentatively assigned as intraligand (IL) pi-->pi* transitions.

Homologues of the Easily Ionized Compound Mo2(hpp)4 Containing Smaller Bicyclic Guanidinates

Two bicyclic guanidinate ligands consisting of 5,5-membered (tbo) and 5,6-membered (tbn) rings have been used for the preparation of dimolybdenum compounds, such as Mo2(tbo)4 and Mo2(tbo)4Cl, and species containing Mo2(tbn)4(n+) with n = 0-2. The compounds with quadruply bonded Mo2(4+) species are strong reducing agents and have potentials of about -1 V (vs Ag/AgCl) for the Mo2(5+/4+) process. The structure of the THF solvate of Mo2(tbo)4 shows the longest Mo-Mo bond distance, 2.1453(4) A, for a quadruply bonded species, and this is due to a large divergent angle induced by the geometry of the ligand. This distance increases to 2.2305(8) A upon oxidation by CH2Cl2 to Mo2(tbo)4Cl. For the 5,6-membered-ring ligand tbn, even though the divergent angle is large compared to formamidinate ligands, it is not as large as that in tbo, and the Mo-Mo distance in Mo2(tbn)4, 2.082(1) A, is in the normal range for paddlewheel Mo2(4+) compounds. This distance increases to 2.2233(8) A upon oxidation by O2 in CH2Cl2, which forms Mo2(tbn)4Cl2 x CH2Cl2.

A paramagnetic precursor for polymeric supramolecular assemblies based on multiply bonded dimetal units: μ-acetato-acetonitriletris(μ-N,N′-diphenylformamidinato)diruthenium tetrafluoroborate dichloromethane hemisolvate

The title compound, [Ru2(C13H11N2)3(C2H3O2)(C2H3N)]BF4.0.5CH2Cl2 or [Ru2(mu-DPhF)3(mu-O2CMe)(MeCN)]BF4.0.5CH2Cl2, where DPhF is N,N'-diphenylformamidinate, crystallized as dark-blue block-shaped crystals. In the unit cell, the diruthenium cation lies on a general position, and the BF4- anions reside on two independent special positions with crystallographic twofold symmetry. Disorder was observed for one of the phenyl groups in the formamidinate ligand, the axial acetonitrile molecule and the interstitial dichloromethane molecule. The compound, which exhibits a long Ru-Ru bond of 2.4131 (5) A, is the first {Ru2}5+ formamidinate species that is both equatorially and axially functionalized so that it can be used as a precursor for polymeric paramagnetic supramolecular assemblies.

Systematic preparation of Mo 2 4+ building blocks for supramolecular assemblies.

The preparation of additional and useful building blocks for the construction of supramolecular entities with quadruply bonded Mo(2)(4+) units has been explored, and five new mixed-ligand complexes with three types of ligands and various basicities are reported. The ligands used were the DAniF (N,N'-di-p-anisylformamidinate) anion, the acetate anion, and neutral acetonitrile molecules. The formamidinate ligands are the least labile, and the acetonitrile molecules are the most labile. This difference as well as a relatively strong trans directing influence by the formamidinate anions in ligand substitution reactions allows designed synthesis of various mixed-ligand building blocks, including rare pairs of cis and trans isomers. The new compounds are cis-Mo(2)(DAniF)(2)(O(2)CCH(3))(2) (1), trans-Mo(2)(DAniF)(2)(O(2)CCH(3))(2) (2), trans-[Mo(2)(DAniF)(2)(O(2)CCH(3))(CH(3)CN(eq)())(2)]BF(4) (3), trans-[Mo(2)(DAniF)(2)(CH(3)CN(eq)())(4)](BF(4))(2) (4), and [Mo(2)(O(2)CH(3))(CH(3)CN(eq)())(6)(CH(3)CN(ax)())](BF(4))(3) (5), where eq and ax designate equatorial and axial ligands, respectively. A comparison with some previously synthesized complexes is given along with a discussion of the overall reactivity of all compounds.

Synthesis and structural characterization of trans-[Mo 2(H 2DMepyF) 2(CH 3CN) 4](BF 4) 6 (HDMepyF= N, N′-di(6-methyl-2-pyridyl)formamidine)

Reaction of Mo 2(O 2CCH 3) 2(DMepyF) 2 (HDMepyF= N, N ′-di(6-methyl-2-pyridyl)formamidine) with HBF 4 in CH 2Cl 2/CH 3CN afforded the complex trans-[Mo 2(H 2DMepyF) 2(CH 3CN) 4](BF 4) 6 ( 1), which crystallized in two forms, trans-[Mo 2(H 2DMepyF) 2(CH 3CN) 4](ax-CH 3CN) 2(BF 4) 6 · 2CH 3CN ( 1a), and trans- [Mo 2(H 2DMepyF) 2(CH 3CN) 4](ax-BF 4) 2(BF 4) 4 · 2CH 3CN ( 1b). The molecular structures of complexes ( 1) consist of two quadruply bonded molybdenum atoms, which are spanned by two trans-bridging formamidinate ligands and coordinated by four trans-CH 3CN. Each H 2DMepyF + ligand adopts an s-cis,s-cis- conformation. The difference between 1a and 1b is that complex 1a contains two CH 3CN molecules as axial ligands, while 1b contains two BF 4 − anions as axial ligands. Complex 1 is the first dimolybdenum complex containing a pair of trans bridging ligands and two pairs of trans-CH 3CN ligands.

Dimolybdenum complexes with mixed formamidinate ligands

Abstract A series of dimolybdenum complexes containing mixed formamidinate ligand are discussed. The reactions of trans-Mo2(O2CCH3)2(o-DMophF)2 [o-HDMophF=N,N′-di(2-methoxyphenyl)formamidine] with N,N′-di(2-pyridyl)formamidine (HDpyF), N,N′-di(2-pyrimidyl)formamidine (HDpmF) and N,N′-di(6-methyl-2-pyridyl)formamidine (HDMepyF), in refluxing CH2Cl2 afforded the complexes, trans-Mo2(O2CCH3)(DpyF)(o-DMophF)2 (1), trans-Mo2(O2CCH3)(DpmF)(o-DMophF)2 (2), and trans-Mo2(O2CCH3)(DMepyF)(o-DMophF)2 (3), respectively. The o-DMophF− and DMepyF− ligands in these complexes adopt the s-cis, s-trans conformation, resulting in Mo–O short distances [2.889 (3) and 2.861(2) A for 1; 2.880(3) and 3.024(4) A for 2], while the DpyF− ligand adopts the s-cis, s-trans conformation, resulting in a Mo–N [3.208(4) A] and a Mo–H [2.90 (3) A] short distances. The reactions of trans-Mo2(O2CCH3)2(o-DMophF)2 with HDMepyF in CH3CN gave complexes 3, trans-Mo2(O2CCH3)(DMepyF)2(o-DMophF) (4), and trans-Mo2(DMepyF)2(o-DMophF)2 (5). The o-DMophF− ligands in 4 and 5 adopt the s-cis, s-cis conformation while DMepyF− assumes an s-cis, s-trans conformation. Complexes 1–5 are the first dimolybdenum complexes containing mixed formamidinate ligands.

Gold(I) Formamidinate Clusters: The Structure, Luminescence, and Electrochemistry of the Tetranuclear, Base-Free [Au4(ArNC(H)NAr)4

The structures of the tetragold(I) formamidinate cluster complexes, [Au4(ArNC(H)NAr)4], Ar=C6H4-4-OMe (1), C6H3-3,5-Cl (2), C6H4-4-Me (3), have been characterized by x-ray crystallography. The range of Au⋅⋅⋅Au distances is 2.8–3.0 A. The angles at Au⋅⋅⋅Au⋅⋅⋅Au are acute and obtuse 70 and 109°, 88 and 91°, and 63 and 116° in 1, 2, and 3, respectively. The four gold atoms are located at the corner of a rhomboid with the formamidinate ligands bridged above and below the near plane of the four Au(I) atoms. The tetranuclear gold(I) complexes show a bright blue-green luminescence under UV light, with an emission at ∼490 nm and a weak emission at ∼530 nm in the solid state, at room temp and 77 K. The oxidation of the formamidinate cluster, 1, has been studied electrochemically in 0.1 M Bu4NPF6/CH2Cl2 at a Pt working electrode with different scan rates. Three waves were obtained, 0.75, 0.95, and 1.09V vs. Ag/AgCl at a scan rate of 500 mV/s, the three waves are reversible. The potentials are independent of the scan rate in the range 50 mV/s to 3 V/s. The current at the third wave is larger than those at the first two.

Chemistry of dimolybdenum complexes containing anions of N,N′-di(6-methyl-2-pyridyl)formamidine (HDMepyF) and carboxylate ligands

Reactions of Mo 2(O 2CCF 3) 4 and Mo 2(O 2C(CH 2) n CH 3) 4 with N,N′-di(6-methyl-2-pyridyl)formamidine (HDMepyF) in CH 2Cl 2 afforded complexes of the types Mo 2(O 2CCF 3) 2(DMepyF) 2, 1, and Mo 2(O 2C(CH 2) n CH 3) 2(DMepyF) 2 ( n=0, 2; n=2, 3; n=5, 4; n=8, 5; n=14, 6), respectively. Their structures have been determined by X-ray crystallography. The molecular structures of complexes 1– 6 consist of two quadruply bonded molybdenum atoms, which are spanned by two trans bridging formamidinate ligands and two trans bridging carboxylate ligands. The formamidinate ligands are coordinated to the Mo centers in bidentate fashions via the two central nitrogen atoms and the two terminal pyridyl rings are dangling. The DMepyF − ligand adopts the s-cis, s-trans-conformation, resulting in a Mo⋯N and a Mo⋯HC short distances. Complex 6 is the first structurally characterized dimolybdenum complex containing carboxylate ligands with the longest alkyl chains.

Structural studies of nickel complexes of the unsymmetrical tridentate ligand N-phenyl- N-(2-pyridyl)formamidinate

We describe the preparation and structural characterization of six nickel complexes with the unsymmetrical formamidine HPhPyF ( N, N′-phenylpyridylformamidine). These six compounds include one dinuclear species Ni 2(PhPyF) 4 ( 1), two mononuclear complexes: cis-[Ni(HPhPyF) 2(MeCN) 2][BF 4] 2 ( 3) and Ni(HPhPyF)Br 2 ( 6), and three trinuclear compounds: Ni 3(PhPyF) 4(MeCN) 2(BF 4) 2 ( 2), [Ni 3(PhPyF) 4Cl]Cl ( 4), and Ni 3(PhPyF) 4Cl 2 ( 5). In the dinuclear species 1, the two nickel atoms are surrounded by four formamidinate ligands. Each is pseudo-octahedral and there is long separation (≈3.41 Å) between them. One mononuclear compound, cis-[Ni(HPhPyF) 2(MeCN) 2][BF 4] 2 ( 3) has a distorted octahedral geometry, the other Ni(HPhPyF)Br 2 ( 6) contains a Ni atom in a pseudo-tetrahedral environment. All three trinuclear compounds contain a linear chain of three Ni II atoms wrapped by four PhPyF anions, but each has a different axial environment. There are two axially coordinated MeCN in 2, only one axial Cl anion for 4 and two axial Cl anions for 5. In 2, 4, and 5, the Ni 3 6+ chains are symmetrical with relatively long Ni⋯Ni separations in the range 2.44–2.51 Å.

Tungsten to tungsten quadruple bonds: over 30 years of research, 50 structurally characterized compounds and 100 known compounds

Since the first reported structure of a quadruply bonded ditungsten complex in 1977, the field of W 2(II, II) chemistry has expanded as new synthetic methodologies have been developed. Based on a recently developed synthetic route in our laboratory, the synthesis and structures of two new W 2(II, II) complexes with substituted formamidinate ligands are reported. With the addition of these two new structures, the number of structurally characterized quadruply bonded W 2(II, II) complexes exceeds 50 and over 100 W 2(II, II) complexes have been synthesized. A compilation of the quadruply bonded W 2(II, II) compounds, W–W bond distances, and synthetic methodologies is presented.

Structural studies of N,N'-di(ortho-fluorophenyl)formamidine group 1 metallation.

The treatment of N,N'-di(ortho-fluorophenyl)formamidine (HFPhF) in tetrahydrofuran with equimolar amounts of n-butyllithium, sodium bis(trimethylsilyl)amide or potassium bis(trimethylsilyl)amide affords the colourless crystalline formamidinate complexes [Li(FPhF)(thf)] (1), [Na(FPhF)(thf)] (2) and [K(FPhF)] (5). Low-temperature preparation of 2 in diethyl ether yields the Et(2)O adduct [Na(FPhF)(Et(2)O)] (3). At ambient temperature the sodium fluoride inclusion complex [Na(3)(FPhF)(3)(Et(2)O)(NaF)] (4) is also formed. Spectroscopic ((1)H, (13)C and (19)F((1)H) NMR) data for 1-5, microanalytical analyses for compounds 1, 2 and 5 and X-ray structure determinations for 1, 3-5 confirm the formulae of these species. In the solid-state, 1 and 3 possess a dimeric nature in which the formamidinate ligands coordinate through mu(2):eta(2):eta(1) (1) and mu(2):eta(2):eta(2) (3) binding modes. These are enabled by partial ortho-fluoro donation. Compound 4, which is also dimeric, contains two trisodium tris(formamidinate) units that comprise mu(2):eta(2):eta(2)-FPhF ligands, a bridging diethyl ether moiety and an unprecedented mu(3):eta(2):eta(2):eta(2)-formamidinate donor. Together, these trinuclear units encapsulate two sodium fluoride units by eta(2)-N,N-formamidinate chelation of the sodium cations (thereby creating further mu(3):eta(2):eta(2):eta(2)-bound formamidinates) and fluoride-sodium interactions. Compound 5 extends the coordinative versatility of FPhF to mu(2):eta(4):eta(3) coordination by the generation of K(2)(mu(2):eta(4):eta(3)-FPhF)(2) units that exhibit eta(2)-arene interactions. Macromolecularly, the overlaying of these units affords a polymeric solvent-free structure that incites coordination of the FPhF ligands to metal atoms above and below the K(2)(FPhF)(2) plane. Overall, this generates a remarkable mu(4):eta(4):eta(3):eta(2):eta(1)-amidinate binding mode that incorporates both bridging and terminal fluorine donors. Compounds 1-5 are the first non-chromium complexes of N,N'-di(ortho-fluorophenyl)formamidinate.

Dicadmium complexes bearing tetradentate formamidinate ligands with triple helical structures

Reactions of Cd(NO 3) 2·4H 2O with bis(2-pyridyl)formamidine (HDpyF) and bis(6-methyl-2-pyridyl)formamidine (HDMepyF) in CH 3OH afforded the dinuclear products, [Cd 2(DpyF) 3][Cd(NO 3) 4] 0.5 ( 1), and [Cd 2(DMepyF) 3](NO 3) ( 2), respectively. Their structures were determined by X-ray crystallography. Complex 1 crystallized in two different space groups with different packing solvents. Both the DpyF − and DMepyF − ligands are coordinated to the Cd atoms in new tetradentate fashions, forming two chelating and four bridging bonding modes. Each cadmium metal center of the cations is tris-chelated and strongly distorted from octahedral coordination due to the small bite of the DpyF − and DMepyF − ligands. The molecules of the cations are chiral due to the ligand constraints. They are the first dicadmium complexes bearing formamidinate ligands with triple helical structures.

Tetrakis[μ-N,N′-bis(4-chlorophenyl)formamidinato-N:N′]dimolybdenum(II)

The title compound, [Mo2(C13H9Cl2N2)4], is a tetra-chelate `paddle wheel' complex of quadruply bonded dimolybdenum(II). Coordination of the four chloro-substituted formamidinate ligands occurs through the ligand N atoms. The centroid of the Mo—Mo bond is located on an inversion center. The Mo—Mo bond length is 2.0899 (12) Å.

Preparation and Structure of Two Ditungsten Compounds Synthesized with the 3,5-Dichlorophenylformamidinate Ligand.

The structure, preparation, and spectroscopy of a W(2)(II, II) paddlewheel complex with four formamidinate ligands is reported. Upon exposure to air and moisture in solution, the W(2)(II, II) core undergoes an oxidative addition reaction to form a W(2)(III, III) edge-sharing bioctahedral (ESBO) complex with two bridging hydroxides. The products, W(2)(&mgr;-DCPF)(4) (1) and W(2)(&mgr;-OH)(2)(&mgr;-DCPF)(2)(eta(2)-DCPF)(2) (2) where DCPF is [(3,5-Cl(2)C(6)H(3))NC(H)N(3,5-Cl(2)C(6)H(3))(-)], were characterized by UV-vis and (1)H NMR spectroscopy. Structural data are presented for W(2)(&mgr;-DCPF)(4) with four bridging formamidinate ligands and W(2)(&mgr;-OH)(2)(&mgr;-DCPF)(2)(eta(2)-DCPF)(2) with the formamidinate ligands in both chelating and bridging positions. Crystallographic data for W(2)(&mgr;-DCPF)(4) (1) and W(2)(&mgr;-OH)(2)(&mgr;-DCPF)(2)(eta(2)-DCPF)(2) (2) are as follows: (1), C(68)H(60)Cl(16)N(8)O(4)W(2), a = 12.6906(3) Å, b = 12.7818(4) Å, c = 13.0450(3) Å, alpha = 109.173(1) degrees, beta = 93.865(1) degrees, gamma = 103.746(1) degrees, triclinic, P&onemacr; (No. 2), and Z = 1 and (2), C(59)H(35)Cl(16)N(8)O(2)W(2), a = 17.1524(1) Å, b = 20.6568(3) Å, c = 19.3959(3) Å, beta = 102.791(1) degrees, monoclinic, C2/c (No. 15), and Z = 4.