Donor-acceptor hydrogen (H)-bonding contributes to good temperature resistance for energetic compounds. Now we report a strategy which maximizes donor-acceptor H-bonding sites in the construction of new energetic compounds. The straightforward...

Three-dimensional molecular architectures self-assembled with tripodal and tetratopic donors are valuable because of their encapsulation properties. Here, we present Co(I)-Fe(II)-Pd(II) heterotrimetallic trifacial barrel 1, which was self-assembled using a newly synthesized tetratopic donor [CpCo(CbR)] [L; Cp = cyclopentadienyl, Cb = cyclobudiene, and R = 4-(4-pyridylphenyl)] and a 90° acceptor [ cis-(dppf)Pd(OTf)] (A1; dppf = (diphenylphosphino)ferrocene and OTf = CFSO). The heterotrimetallic barrel 1 exhibited selective 1:1 interaction with a N, N'-dimethyl-1,4,5,8-naphthalenetetracarboxylic diimide guest, as revealed by H NMR analysis. The self-assembly of donor L with two other Ru(II)-based 180° acceptors [( p-cymene)Ru(OO∩OO)(OTf)] [OO∩OO = 6,11-dioxido-5,12-naphthacenedione (A2) and oxalate (A3)] resulted in tetragonal-prismatic cages. Self-assembly using the longer acceptor A2 provided rare isomers of a tetragonal-prismatic cage by varying the orientation of the cyclopentadienyl moiety out-out (2) or out-in (2) of the cavity, whereas self-assembly using the shorter acceptor A3 selectively resulted in the tetragonal-prismatic cage 3. The three-dimensional molecular architectures 1-3 were characterized by combined spectroscopic and elemental analyses. The structures of molecular barrel 1 and prismatic cage 3 were elucidated by single-crystal X-ray analysis.

Reactions of {η 5 -C 5 H 4 [C(O)Cl]}Co(η 4 -C 4 Ph 4 ) and {η 5 -C 5 H 4 [C(O)Cl]}Fe(η 5 -Cp) with 8-aminoquinoline resulted in cobalt and iron sandwich derived carboxamides.The reaction of these carboxamides with Pd(OAc) 2 in acetonitrile resulted in αC−H activation of the Cp rings of the sandwich compounds and formation of novel palladacycles 3 and 4, having both N−H and one α-C−H hydrogen atom of the Cp ring displaced and palladium forming a square planar complex with acetonitrile as the fourth ligand. These air-stable palladacycles reacted with MeI and EtI in acetic acid, resulting in monoand 2,5-di-α-alkylated sandwich carboxamides, thereby providing a new method to realize Cp-multisubstituted sandwich compounds. Selectivity in α-substitution was observed in the presence of NaHCO 3 . The cobalt sandwich carboxamide 1, the new palladacycles 3 and 4, and the 2,5-dimethylated cobalt sandwich carboxamide 5 have also been structurally characterized using single-crystal X-ray structural studies.

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Polynitro compounds exhibit high density and good oxygen balance, which are desirable for energetic material applications, but their syntheses are often very challenging. Now, the design and syntheses of a new three-dimensional (3D) energetic metal–organic framework (EMOF) and high-energy-density materials (HEDMs) with good thermal stabilities and detonation properties based on a polynitro pyrazole are reported. Dipotassium 3,5-bis­(dinitromethyl)-4-nitro-1H-pyrazole (5) exhibits a 3D EMOF structure with good thermal stability (202 °C), a high density of 2.15 g cm–3 at 100 K (2.10 g cm–3 at 298 K) in combination with superior detonation performance (D v = 7965 m s–1, P = 29.3 GPa). Dihydrazinium 3,5-bis­(dinitromethyl)-4-nitro-1H-pyrazole (7) exhibits a good density of 1.88 g cm–3 at 100 K (1.83 g cm–3 at 298 K) and superior thermal stability (218 °C), owing to the presence of 3D hydrogen-bonding networks. Its detonation velocity (8931 m s–1) and detonation pressure (35.9 GPa) are considerably superior to those of 1,3,5-trinitro-1,3,5-triazine (RDX). The results highlight the syntheses of a 3D EMOF (5) and HEDM (7) with five nitro groups as potential energetic materials.

Palladium catalyzed bis-arylations, -alkylations, and -allylations on the Cp ring of iron and cobalt sandwich compounds have been achieved using the bidentate picolinamide directing group. This directing group along with catalytic Pd­(OAc)2 was found to be highly efficient for C–H functionalization, giving up to 87% yields. The palladacyclic intermediate for the C–H activation of the Cp ring has been isolated and structurally characterized for the cobalt sandwich compound [η5-C5H5]­Co­(η4-C4Ph4). Attempted C–H annulation reactions using picolinamide-derived sandwich compounds did not yield the expected annulated products and instead oxidized the Cp- and picolinamide-bound CH2 unit to aldehydes. Detailed studies on this novel and unprecedented oxidation indicated that this happens only with the assistance of the picolinamide directing group. We have also shown that the sp2 C–H functionalization and the sp3 C–H oxidation can be effectively carried out as a one-pot reaction.

Carbon–heteroatom bond formation in metal-sandwich compounds using C–H activation by selective directing groups.

Reaction of in situ generated {η 5 -[MeOC(O)]C 5 H 4 }Co(PPh 3 ) 2 with methyl 3-phenyl-2-propynoate followed by diphenylacetylene in refluxing toluene resulted in the formation of the cobalt sandwich compound {η 5 -[MeOC(O)]C 5 H 4 }Co{η 4 -C 4 Ph 3 [C(O)OMe]} (1), having methyl ester units on both the cyclopentadienyl (Cp) and cyclobutadiene (Cb) rings. Hydrolysis of the ester groups using aqueous KOH resulted in the dicarboxylic acid {η 5 -C 5 H 4 [C(O)OH]}Co{η 4 -C 4 Ph 3 [C(O)OH]} (2). The dicarboxylic acid 2 was converted to the novel bis(oxazolinyl) derivative [η 5 -(4-iPr-2-Ox)C 5 H 4 ]Co[η 4 -C 4 Ph 3 (4-iPr-2-Ox)] (3; Ox = oxazolinyl) by its reaction with oxalyl chloride, (S)-2-amino-3-methyl-1-butanol, triethylamine, and mesyl chloride. Reaction of the chiral bis(oxazoline) ligand 3 with Pd(OAc) 2 in acetic acid at 60 °C resulted in the formation of the novel chiral palladacycle 4, resulting from an unprecedented cyclopalladation involving one of the cyclobutadiene-bound phenyl groups. Palladacycle 4 has two trans-oriented oxazolinyl units and one of the phenyl groups of the cyclobutadiene ring bound to the palladium center along with an acetyl group. The reaction of KX (X = Br, I) with 4 in acetone− water medium yielded the bromo-and iodo-derived chiral palladacycles 5a,b. Compounds analogous to 3 having a chiral oxazolinyl unit on the Cb ring and a methyl or acetyl unit on the Cp ring, (η 5 -RC 5 H 4 )Co(η 4 -C 4 Ph 3 R′) (R′ = oxazolinyl; R = acetyl (8a), methyl (8b)) were also prepared and characterized. Analogous reactions of 8a,b with 1.5 equiv of Pd(OAc) 2 in acetic acid at 60 °C gave the chiral palladacycles 9a,b. Analysis of these compounds indicated that, in contrast to the monomeric chiral palladacycle obtained from the reaction of 3, compounds 9a,b are molecules with a unique linear tetraacetate-bridged tripalladium core having the two cyclopalladated cobalt sandwich units at the periphery. Structural analysis of 9a indicated that the molecule possesses the same type of seven-membered palladacycle observed in the cases of 4 and 5a,b.