Methyleneimine CH2dNH as a Unidentate Ligand in Rhenium Complexes This work was supported by MIUR (Rome)—Programmi di Ricerca Scientifica di Rilevante Interesse Nazionale, Cofinanziamento 2000–2001. We thank Daniela Baldan for technical assistance.

Abstract

Coordinated hydrazines RNHNH 2 are reported to react with oxidizing agents, such as [Pb(OAc) 4 ] and H 2 O 2 , to give the corresponding diazenes RN NH, the stabilization of which on an appropriate metal fragment allows their separation as coordinated species. [1±3] We now report a new reaction of coordinated methylhydrazine, which reacts with [Pb(OAc) 4 ] to give a h 1 -NHCH 2 methyleneimine derivative.The CH 2 NH molecule is a reactive species which was first obtained in 1933 from the low-temperature reaction of HCN with hydrogen. [4] It has been detected in several galactic objects [5] and proposed as a possible precursor [6] of the simplest a-amino acid, glycine. As a ligand, it is present in only one case, through p coordination [7] to an osmium center; no other report has been found on this molecule, which displays a simple constitution and structure, and has still unknown properties.The reaction of the hydride [8] [ReH(CO){P(OEt) 3 } 4 ] with triflic acid (TfOH) gives the thermally unstable [Re(h 2 -H 2 )(CO){P(OEt) 3 } 4 ] (CF 3 SO 3 ) À species, which loses H 2 , affording the compound [Re(k 1 -OTf)(CO){P(OEt) 3 } 4 ]. Substitution of the weakly bound triflato ligand with methylhydrazine gives trans-[Re(CH 3 NHNH 2 )(CO){P(OEt) 3 } 4 ] (1), which was isolated as a BPh 4 salt (1-BPh 4 ) in about 70 % yield (Scheme 1). Complex 1-BPh 4 was characterized by standard methods (IR, NMR, L M , elemental analysis). The IR spectra show the n NH bands at 3343 and 3291 cm À1 of the methylhydrazine OC Re P P P P H OC Re P P P P NH 2 NHCH 3 1 OC Re P P P P OTf TfOH, -80 °C -H 2 excess CH 3 NHNH 2 -OTf -+ Scheme 1. P P(OEt) 3 .ligand, whereas the 1 H NMR spectrum exhibits resonance signals at d 4.35 (s, br; ReNH 2 NHCH 3 ), 3.93 (m, br; ReNH 2 NHCH 3 ), and 2.49 ppm (d; ReNH 2 NHCH 3 ) of the CH 3 NHNH 2 group.Treatment of methylhydrazine complex 1-BPh 4 with an equimolar amount of [Pb(OAc) 4 ] at low temperature (À 40 8C) in CH 2 Cl 2 gives a mixture of methyldiazene [Re(CH 3 N NH)(CO){P(OEt) 3 } 4 ]BPh 4 (2-BPh 4 ) and methyleneimine [Re(h 1 -NH CH 2 )(CO){P(OEt) 3 } 4 ]BPh 4 (3-BPh 4 ) derivatives (Scheme 2). These were separated by fractional crystallization in moderate yields (42 % for 2-BPh 4 , 24 % for 3-BPh 4 ) as analytically pure white crystalline solids.

Formation of a Methyleneimine Moiety by Reaction of a RuII‐Coordinated Azide Ion with Methyl Iodide

“…This coordination fashion is similar to that of the reported κN ‐mode coordination rhenium complex 10c. The N1C1 bond length, 1.202(16) Å, is shorter than those of other structurally characterized imine moieties coordinated to a metal center (1.25–1.31 Å) 10c. 11 The acetonitrile ligand linearly coordinates to the metal center, as in previously reported Ru II complexes 11b.…”

“…The methyleneimine ligand coordinates to the ruthenium center in a bent fashion with Ru‐N1‐C1=135.4(7)° and with RuN1=2.083(10) and N1C1=1.202(16) Å. This coordination fashion is similar to that of the reported κN ‐mode coordination rhenium complex 10c. The N1C1 bond length, 1.202(16) Å, is shorter than those of other structurally characterized imine moieties coordinated to a metal center (1.25–1.31 Å) 10c.…”

“…A few metal complexes containing a methyleneimine moiety (NHCH 2 ) have been synthesized by the reaction of a methylhydrazine or methylimido complex 10. The NHCH 2 ligand coordinates through two coordination modes; one is the N‐monodentate mode ( κN ) of a rhenium complex10a–c and another the N , C ‐bidentate one ( κ 2 N , C ) of an osmium complex 10d. Only one rhenium complex containing an methyleneimine‐ κN moiety has been characterized by X‐ray crystallography 10c.…”

“…The NHCH 2 ligand coordinates through two coordination modes; one is the N‐monodentate mode ( κN ) of a rhenium complex10a–c and another the N , C ‐bidentate one ( κ 2 N , C ) of an osmium complex 10d. Only one rhenium complex containing an methyleneimine‐ κN moiety has been characterized by X‐ray crystallography 10c. Herein, we describe the reaction of cis ‐[Ru(N 3 ) 2 (bpy) 2 ]⋅H 2 O (bpy=2,2′‐bipyridine) with CH 3 I in CH 3 CN to give a rare methyleneimine complex of ruthenium( II ) (Ru–NHCH 2 ) and its characterization by IR and NMR spectroscopy and X‐ray crystallography.…”

Synthesis and Reactivity of Ruthenium Azido Complexes Containing a Hydridotris(pyrazolyl)borate Ligand and Dimerization of Terminal Alkynes in Organic and Aqueous Media

“…The allylimine ligand coordinates to the ruthenium center in a bent fashion with Ru−N7−C12 = 130.9(3)° and with Ru−N7 = 2.036(3) and N7−C12 = 1.282(5) Å. This coordination fashion is similar to that of the reported κN-mode coordination rhenium complex . Interestingly, the Ru−N7−C12 and N7−C12−C13 angles, 130.9(3) and 125.6(5)°, respectively, are remarkably large.…”