Reaction of
trans-(dmpe)
2CrCl
2 (dmpe = 1,2-bis(dimethylphosphino)ethane) with one equivalent of LiCCSiMe
3 and one equivalent of
nBuLi in THF under a dinitrogen atmosphere affords dark orange
trans,trans-[(Me
3SiCC)(dmpe)
2Cr]
2(
µ-N
2)·hexane (
1). Under similar conditions but in the absence of acteylide ligand, the reaction of
trans-(dmpe)
2CrCl
2 with 2 equivalents of
nBuLi yields the previously characterized complex
trans-(dmpe)
2Cr(N
2)
2 (
2), while the reaction of
trans-(dmpe)
2CrCl
2 with 2 equivalents of LiCCSiMe
3 in THF yields
trans-(dmpe)
2Cr(CCSiMe
3)
2 (
3). Compound
3 can also be synthesized by irradiating a mixture of
trans-(dmpe)
2CrMe
2 and HCCSiMe
3 or by reduction of HCCSiMe
3 with compound
2. The magnetic properties, electrochemistry, and
crystal structure of
trans,trans-[(Me
3SiCC)(dmpe)
2Cr]
2(
µ-N
2) are consistent with the complex containing two Cr
I ions bridged by a neutral N
2 moiety, with a 1.178(10) Å N
N bond distance. For complex
1 redox processes centered at
E1/2 = &
ndash;1.69 V (Δ
Ep = 185 mV) and &
ndash;1.43 V (Δ
Ep = 182 mV) versus Fe(Cp)
2/Fe(Cp)
2+ are assigned to the Cr
ICr
I/Cr
ICr
II and Cr
ICr
II/Cr
IICr
II couples, respectively. For
trans-(dmpe)
2Cr(CCSiMe
3)
2 a reversible couple assigned as the Cr
II/III couple was observed at &
ndash;1.59 V (Δ
Ep = 242 mV) versus Fe(Cp)
2/Fe(Cp)
2+. The dinuclear Cr(I)−dinitrogen complex
1 has a room temperature magnetic moment of 2.77 µ
B while compound
3 displays a moment of 2.55 µ
B. Density-functional theory calculations performed on a model compound of
1, namely,
trans,trans-[(HCC)(dpe)
2Cr]
2(
µ-N
2) (dpe = diphospinoethane), indicate that oxidation of the molecule should result in weakening of the dinitrogen triple bond.