Isolation and spectral studies of water-soluble η⁵-cyclichydrocarbon rhodium and iridium complexes with pyridyl diketone analogues bonded through κ²-N∩O, κ⁴–N∩O, and κ³-N-C-N modes

Abstract

The reaction of [M(µ-Cl)Cl]₂ (M = Rh, Ir;  = η ⁵-C₅Me₅) with 1-phenyl-3-(2-pyridyl)propane-1,3-dione (pppdH) and 1,3-di(2-pyridyl)propane-1,3-dione (dppdH) in 1 : 2 and 1 : 1 molar ratio, respectively, yielded corresponding monomeric complexes [M(κ ²-N-O-pppdH)Cl]⁺ [M = Rh (1), Ir (2)] and dimeric complexes [()₂M₂(κ ⁴-N-O-dppd)Cl₂]⁺ [M = Rh (3), Ir (4)]. The treatment of [Ir(µ-Cl)Cl]₂ with dppdH in 1 : 2 molar ratio yielded the activated monomeric complex [Ir(κ ³-N-C-N-dppd)]⁺ (5). The formation of a C(sp³)–H is attributed to softer iridium, whereas Rh precursor yielded only the corresponding dimer 3. The formation of these complexes has been established by IR and NMR spectroscopic data and elemental analysis. Molecular structures of 2, 3, and 5 have been confirmed by single-crystal X-ray diffraction. The enolic “O–C–C–C–O” fragment of the coordinated ligand is neutral (κ ²-N-O-pppdH) in monomeric 1 and 2 and neutral as well as concomitantly uninegative (κ ⁴-N-O-dppd) in dimeric 3 and 4. In C–H-activated monomeric complex 5, the “O–C–C–C–O” fragment is in ketonic form with (κ ³-N-C-N-dppd) bonding of the ligand.

Keywords:

• 1-Phenyl-3-(2-pyridyl)propane-1,3-dione
• 1,3-Di(2-pyridyl)propane-1,3-dione
• Rhodium
• Iridium
• Pentamethylcyclopentadienyl
• C–H activation

Acknowledgments

S.L. Nongbri thanks UGC-RGNF for financial support in the form of SRF bearing fellowship allotment No. 18-16(7)/Acad/2009-77. K.M. Rao gratefully acknowledges financial support from the CSIR, New Delhi, through the Research grant No. 01(2493)/11/EMR-II.