The hydrazine complexes [Re(RNHNH 2 )(CO) n P 5−n ]BPh 4 [R = H, CH 3 , Ar; n = 1−4; P = P(OEt) 3 , PPh(OEt) 2 , PPh 2 OEt] were prepared by allowing the hydride species [ReH(CO) n P 5−n ] to react first with a Brønsted acid and then with hydrazine. The reaction of either [Re(NH 2 NH 2 )(CO) n P 5−n ]BPh 4 or [Re(ArNHNH 2 )(CO) n P 5−n ]BPh 4 with Pb(OAc) 4 at −40°C proceeds with the selective oxidation of the hydrazine ligand to yield either [Re(NH=NH)(CO) n P 5−n ]BPh 4 or [Re(ArN=NH)(CO) n P 5−n ]BPh 4 . The oxidation of [Re-

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.

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.