Synthesis and Crystal and Molecular Structure of [{Hydroboratotris(3'-phenylpyrazolyl)}indium]: An Air-Stable Monomeric Indium(I) Complex

Abstract

As part of our work on the chemistry of the heavier members of group 13, we recently synthesized and structurally characterized [ bis(hydroboratotris(3,5-dimethylpyrazolyl)}indium(III)]iodide (2) and [bis(methylgallatotris(pyrazolyl))indium(III)]- [In141 (3).1 Recognizing the formal analogy between the hydroboratotrispyrazolyl anion HB(Pz)3-(and its pyrazolylsubstituted derivatives) and the cyclopentadienyl anions C5R5-(R = H, CH3),2 we were led to claim 2 and 3 as analogues of the unknown "indocene" cations [$-(C5R5)2In]+. A characteristic of the cyclopentadienyl anions is their ability to stabilize metals in low oxidation states, e.g., In(CsH5)3and the recently synthesized Ga(C5H5)4 and A14(C~R5)4.5 It seemed to us that synthesis of an In1 complex with HB(Pz")~-(Pz" = a substituted pyrazole) would strengthen the analogy between hydroboratotris(pyrazoly1) anions and cyclopentadienyl anions and also significantly extend the chemistry of In a previous study, we observed thegradual disproportionation of In1 to In111 and In in the presence of HB(PZ*)~-(Pz* = 3,s-dimethylpyrazole) on slowly raising the temperatureofthe reactantsfrom-30 OC to ambient.' We argued that use of a more sterically hindered pyrazole than Pz* might facilitate the isolation of a stable In1 species. On reacting indium iodide with HB(Pz**),-(Pz** = 3-phenylpyrazole) in tetrahydrofuran at -50 OC, we were able to isolate colorless, blocklike crystals. The mass spectra, lH and 13C N M R spectra, and elemental analyses indicated these crystals to be [I~-(HB(Pz**)~)] (1). This was confirmed by an X-ray structural study.'The structure of 1 is shown in Figure l a and b, and comparisons between it and related compounds are shown in Table 1. Whereas the geometry about the metal in 2 and particularly 3 is very close tooctahedral, in 1 the In adopts a pyramidal geometry with respect to the coordinated nitrogen atoms. This arrangement is also seen in 5. The In-N distance in 1 is longer than the corresponding distances in 2 and 3, as expected, and exceeds the sum of the covalent radii by about 8%. There is no In-In interaction in 1, the closest contacts being 6.5 A. The In-In distance in In(CSH5) ( 1 ) Frazer, A.; Piggott, B.; Harman, M.; Mazid, M.; Hursthouse, M. B. A, a = fi = 90°; y = 120°, V = 1255.66 A', and Z = 2(d,ld= 1.471 gmcm-'),p(MoKa) =9.353cm-';absorptioncorrection DIFABS; 5963 reflections, 1910 unique; 1837 with Fo > 3u(F0) were used in the refinement; R = 2.6, R, = 3.5. (8) Cowley, A. H.; Carrano, C. J.; Geerts, R. L.; Jones, R. A.; Nunn, C. M. Angew. Chem., Ini. Ed. Engl. 1988, 27, 277-278. (9) Cowley,A.H.;Geerts, R.L.;Nunn,C.M.;Trofimenko,S.J. Organomet. Chem. 1989, 365, 19-22.U Figure 1. (a, top) Structureof hydroboratotris(3-phenylpyrazolyl)indium, showing the atom-labeling scheme. (b, bottom) Hydridoboratotris(3-phenylpyrazoly1)indium viewed down the 3-fold axis.Table 1. Selected Bond Lengths and Angles for 1 and Related Compounds compd In-N distance (A) N-In-N angle (deg) 1 2.430(4) 78.2(2) 2 2.225(5) 94.6(2), 85.4(2) 2.273(5) 96.1(2), 8...

Bulky Amidinate Complexes of Indium(III). Synthesis and Structure of [CyNC(tBu)NCy]2InCl

“…Because bulky groups are known to stabilize a reduced In center, we attempted the reduction of 1 with Na/C 10 H 8 as shown in Scheme . The product of this reaction, 3 , possessed only the NMR resonances for equivalent dicyclohexylamidinate ligands.…”

Steric and electronic factor comparisons in hydrotris(3-phenylpyrazolyl)borate nickel(II) aryloxides

“…Hydrotris(3-phenylpyrazolyl)borate (Tp Ph ) has been utilized as a model for the active sites of various metalloenzymes (Kawabata et al, 1995;Halcrow et al, 1997;Perkinson et al, 1991;Kremer et al, 1997) and as a reagent for DNA binding and cleavage (Dhar et al, 2002). Tp Ph has also been used as a convenient scaffold for metal-mediated chemistry (Slugovc et al, 2000a;Darensbourg et al, 1996Darensbourg et al, , 2004Chisholm et al, 2000), for systematic 113 Cd chemical-shift studies (Reger et al, 1995), and for the synthesis of unusual compounds (Slugovc et al, 2000b;Frazer & Piggott, 1994; Multi-scan (SADABS; Bruker, 2002) Multi-scan (SADABS; Bruker, 2002) Multi-scan (SADABS; Bruker, 2002 Darensbourg et al, 1995Darensbourg et al, , 1996Siemer et al, 2001;Eichhorn & Armstrong, 1990). Although nickel(II) is biologically relevant and the similar compound [hydrotris(3-phenyl-5-methylpyrazolyl)borato](2,6-isopropylphenolato)nickel(II) was reported to have activity similar to 2,4,5-trihydoxyphenylalanine quinone cofactor (Deb et al, 2012), surprisingly, other than recently reported complexes with simple inorganic ligands (Frampton et al, 2015) 2.…”

X-Ray crystallographic structure of Ga8(pz)12O4Cl4·2thf: a novel gallium pyrazololate complex with a Ga4O4 core

“…In previous publications we drew attention to two significant features of some trispyrazolyl derivatives of group 13 [specifically HB(3-Bu t Pz) 3 2 and HB(3-PhPz) 3 2 ], namely their stabilisation of low oxidation states and their redox properties with main-group metals. 8,9 We now identify a third significant feature of a member of this class of ligand [specifically MeGa(pz) 3 2 ], viz. heterocubane formation.…”