New Complexes of Niobium(V) and Tantalum(V) with Monoanionic NNO Heteroscorpionate Ligands

Abstract

A new synthetic route based on bis(3,5-dimethylpyrazol-1-yl)acetic acid (Hbdmpza) (1) has afforded the alcohol 2,2-bis(3,5-dimethylpyrazol-1-yl)ethanol (Hbdmpze) in good yield. This alcohol and the related lithium compound [{Li(bdmpza)(H 2 O)} 4 ] are excellent precursors for introducing these scorpionate ligands into transition metal complexes.

Tin(IV) and organotin(IV) derivatives of bis(pyrazolyl)acetate: Synthesis, spectroscopic characterization and behaviour in solution.

“…The presence of the COO moiety is indicated by strong m asym (COO) bands in the range 1610-1770 cm À1 , a red shift relative to the free neutral ligands being observed upon complex formation [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. This is in keeping with an electron flow from the ligand toward the tin moiety, with consequent decreasing C@O bond order.…”

“…Bis(pyrazolyl)acetates can be easily deprotonated, 0022 behaving in the anionic form as N,N,O-tripodal donors, similar to tris(pyrazolyl)borates; alternatively they may react in the neutral form like the tris(pyrazolyl)alkanes. Until now, all metal derivatives reported contain bis(pyrazolyl)acetates in the anionic form [3][4][5][6][7][8][9][10][11][12][13]; only a few organometallic derivatives have been reported, limited to Nb, Re, Mn and Cr carbonyls [14][15][16][17][18][19] and a short communication on the crystal structure of Ph 2 SnBr(bdmpza) (bdmpzaH = bis(3,5-dimethylpyrazol-1-yl)acetic acid) [20].…”

Well-Defined Alkyl Heteroscorpionate Magnesium Complexes as Excellent Initiators for the ROP of Cyclic Esters

“…During the past decade, our research group has contributed widely to the design of new “heteroscorpionate” ligands related to the bis(pyrazol-1-yl)methane system, with several pendant donor arms such as carboxylate, dithiocarboxylate, methoxy, cyclopentadienyl, acetamidate and thioacetamidate groups, and, more recently, amidinate groups. It is well known that heteroscorpionate ligands have proved to be excellent ancillary ligands for the synthesis of a variety of organometallic early transition metal complexes. − We have now turned our attention to the exploration of the reactivity of the recently reported amidinate-based heteroscorpionate ligands 17 as convenient ancillary ligands for the synthesis of alkyl-containing magnesium complexes.…”

10 Vanadium, niobium and tantalum

“…41 Heteroscorpionate ligands have also been shown to stabilise niobium imido, and niobium and tantalum chloro complexes. 42,43 Vanadium-oxo complexes supported by ring-contracted porphyrinoids have been synthesised, and IR and resonance-Raman data support a triply-bonded V-oxo interaction. 44 The use of the cyclen macrocycle has been shown to result in the seven-coordinate complex [V(CN) 3 (cyclen)] and also the tetrahedral cage [V 4 (cyclen) 4 (CN) 6 ] 6+ , in which antiferromagnetic coupling leads to an S = 0 ground state.…”