Structural Characterization of Paramagnetic Octahedral Homoscor‐Pionate (Polypyrazolylborate) Cobalt Complexes by ¹H and ¹³C NMR Spectroscopy and by FAB‐Mass Spectrometry

Abstract

ABSTRACT'H and 13C NMR spectroscopy as well as the FAB mass spectrometry have been applied to six bis[tris(pyrazol-1 -yl)borates]Co(ll) and one bis[tetrakis(pyrazol-1 -yl)borate]Co(ll). These octahedral complexes are paramagnetic and it was therefore very difficult to obtain their 13C NMR. The isotropic shifts are very large and characteristic of the different positions of the pyrazole and the boron substituents. FAB-MS also is an interesting method to characterize these complexes, since they give abundant molecular ions and specific fragmentation. INTROD UCTl ONWe have been interested in the characterization of poly(pyraz0l-1 -yl)borates (usually potassium or thallium salts) (1-31 by lH, llB, 13C and 15N NMR spectroscopies. In this paper we will describe the NMR (l H, 136) and MS behaviour of their paramagnetic cobalt(l1) complexes. Concerning l H NMR spectroscopy, some of these octahedral complexes have been carefully studied by Du Pont scientists (Jesson, Domaille, Trofimenko) [4-101 and thus, in the present work, the 'H chemical shifts will be reported and compared with those of Jesson [4]. ' RConcerning 13C NMR spectroscopy, only a comment about the difficulty to observe 13C signals in a Co(ll) complex of bis(pyrazo1-1 -yl)borate derivative has been reported [ l 11.As far as MS is concerned, the information is very scarce and no significant result is worth reporting. In this paper, the FAB method of ionization was selected since it is one of the best for studying polar compounds [12] including organometallic derivatives [la].The seven compounds which will be discussed in this paper are shown below: 1, R = R3= % = R5 = H 2, R = CH2CH2CH2CH3, R3 = R4 = R5 = H 3, R = CH2CH2CH2SCH3, R3 = R4 = R5 = t 4, R = C & j , R3 = R4 = R5 = H 6, R = H, R3 = R5 = CH3, R4 = H 7, R = H, R3 = R4 = R5 = CH3 5, R = pyrazol-1-yl, R3 = R4 =R5=H -473 -

Paramagnetic Pyrazolylborate Complexes Tp2M and Tp*2M: 1H, 13C, 11B, and 14N NMR Spectra and First-Principles Studies of Chemical Shifts

“…Aubagnac et al have reported somewhat different 13 C NMR data . Their signal assignment has not been explained and is at variance with that in Table .…”

A theoretical multinuclear NMR study of pyrazolylborates

“…Alone or in collaboration with Trofi menko we have devoted several papers to these compounds (Aubagnac et al , 1991 ;L ó pez et al, 1994 ;Aubagnac et al , 1995 ;L ó pez et al, 1995 ;Janiak et al 1996 ;Sanz et al , 1996 ;Claramunt et al , 2004a , b ;Santa Mar í a et al, 2007;Trofi menko et al , 2007 ). Alone or in collaboration with Trofi menko we have devoted several papers to these compounds (Aubagnac et al , 1991 ;L ó pez et al, 1994 ;Aubagnac et al , 1995 ;L ó pez et al, 1995 ;Janiak et al 1996 ;Sanz et al , 1996 ;Claramunt et al , 2004a , b ;Santa Mar í a et al, 2007;Trofi menko et al , 2007 ).…”

Synthesis and Properties of Poly(pyrazolyl)borate and Related Boron-Centered Scorpionate Ligands. Part A: Pyrazole-Based Systems

“…A different route employs organoborohydrides RBH 2 or LiRBH 3 [101], obtained from reaction of the corresponding boronic acids RB(OH) 2 with LiAlH 4 [102], in the reaction with pyrazolate ion and excess pyrazole [103]. It is noteworthy that the lithium and thallium salts of the tert-butyl-tris (3- 3 ] -(R = H, Me, i Pr, t Bu, Ph), have been prepared and characterized; because of steric congestion at the boron center, the reaction between Li[ t BuBH 3 ] .…”