Oxidative assembly of octahedral nickel(II)-tris(3,5-dimethylpyrazol-1-yl) methane (Tpm*) complexes by reaction of Ni(COD)2 (COD = 1,5-cyclooctadiene) with putative oxene and nitrene precursors

Article abstract of DOI:10.1016/j.poly.2012.10.034

Reactions of [Ni⁰(COD)₂] (COD = 1,5-cyclooctadiene) with meta-chloroperoxybenzoic acid, phenyl-N-tosylimidoiodinane or 2-(tert-butylsulfonyl)iodosylbenzene were performed in THF solution in the presence of one equivalent of tris(3,5-

Full text of DOI:10.1016/j.poly.2012.10.034

Accepted Manuscript
Oxidative assembly of octahedral nickel(II)-tris(3,5-dimethylpyrazol-1-
yl)methane (Tpm∗)complexes by reaction of Ni(COD) (COD = 1,5-cyclooc‐
2
tadiene) with putative oxene and nitrene precursors
Shengwen Liang, Swarup Chattopadhyay, Jeffrey L. Petersen, Victor G. Young,
Michael P. Jensen
PII:
S0277-5387(12)00805-4
DOI:
http://dx.doi.org/10.1016/j.poly.2012.10.034
POLY 9731
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
25 May 2012
16 October 2012
Please cite this article as: S. Liang, S. Chattopadhyay, J.L. Petersen, V.G. Young, M.P. Jensen, Oxidative assembly
of octahedral nickel(II)-tris(3,5-dimethylpyrazol-1-yl)methane (Tpm∗)complexes by reaction of Ni(COD) (COD
2
= 1,5-cyclooctadiene) with putative oxene and nitrene precursors, Polyhedron (2012), doi: http://dx.doi.org/10.1016/
j.poly.2012.10.034
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Oxidative assembly of octahedral nickel(II)-tris(3,5-dimethylpyrazol-1-yl)methane (Tpm*)complexes by
reaction of Ni(COD)2 (COD = 1,5-cyclooctadiene) with putative oxene and nitrene precursors
Shengwen Liang,a Swarup Chattopadhyay,a,† Jeffrey L. Petersen,b Victor G. Young, Jr.c and Michael P. Jensena,*
(a) Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701 United States, (b) C. Eugene
Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506 United States, (c)
X-ray Crystallographic Facility, Department of Chemistry, University of Minnesota, Minneapolis, Minnesota
55455 United States.
Abstract.
Reactions of [Ni0(COD)2] (COD = 1,5-cyclooctadiene) with meta-chloroperoxybenzoic acid, phenyl-N-
tosylimidoiodinane or 2-(tert-butylsulfonyl)iodosylbenzene were performed in THF solution in the presence of one
equivalent of tris(3,5-dimethylpyrazol-1-yl)methane (Tpm*), yielding the product complexes [Tpm*NiII(OH2)(3-
ClC6H4CO2)2] (2), [(Tpm*)2NiII][Ni(NHTs)4] (3), and [Tpm*NiII(OH)2(OH2)] (4), respectively. Products 2-4 arise
from oxidation of solvated [Ni0(COD)2], with subsequent ligation of Tpm* and substrate fragments leading to
assembly of disparate octahedral nickel(II) centers. For comparative purposes, the previously reported complex
[(Tpm*)NiII(OH2)Cl2] (1) was also obtained from Tpm* and NiCl2. All complexes were characterized
spectroscopically, and complexes 1-3 were also structurally characterized by X-ray crystallography.
1.0 Introduction
The oxo wall formalism rationalizes the lack of tetragonal oxo complexes for transition metals to the right
of the iron triad to occupancy of π* orbitals, which reduces metal-oxo bond order [1]. Nonetheless, late transition
metal oxo complexes have been reported in non-tetragonal geometries [2,3]; also of interest in this regard are
isolobal CR2, NR, and PR moieties in linear Ni(II) [4], trigonal Ni(II) [5-8] and trigonal Ni(III) complexes [9,10].
Having prepared a number of pseudotetrahedral nickel(II) complexes supported by anionic hydrotris(3,5-
dimethylpyrazol-1-yl)borate (i.e., Tp*Ni-X) [11], and noting isolobal and isoelectronic relationships to a
hypothetical oxo-Ni(II) complex supported the neutral carbon-collared analog tris(3,5-dimethylpyrazol-1-
yl)methane (Tpm*) [12], we reasoned that a straightforward approach to [(Tpm*)NiII(O)] or an isolobal imido
† Current address: Department of Chemistry, University of Kalyani, West Bengal, India
* Corresponding author. Tel: +1 (740) 593-1745. FAX: +1 (740) 593-0148. E-mail address: jensenm@ohio.edu

2
analog [(Tpm*)NiII(NR)] would be addition of Tpm* to [Ni0(COD)2] [13], and subsequent reaction with an oxene or
nitrene precursor. A species such as [(Tpm*)NiII(O)] might be subsequently oxidized to a Ni(III) state stabilized by
enhanced oxonickel bond order [14]. Similar high-valent species have been invoked as intermediates in peroxide-
driven epoxidations and hydroxylations [15-18], and dimeric [TpNiIII(µ-O)]2 complexes have been isolated [19-23].
Tpm* was added accordingly to [Ni0(COD)2] (COD = 1,5-cyclooctadiene) in THF, and then meta-
chloroperoxybenzoic acid (mcpba), phenyl-N-tosylimidoiodinane (PhINTs; Ts = tosyl, SO2C6H4-4-CH3) or 2-(tert-
butylsulfonyl)iodosylbenzene (ArIO) were added in separate reactions. Our strategy was only partially successful;
oxidation of [Ni0(COD)2] and assembly of Tpm*-supported nickel(II) complexes occurred readily in each case,
however the targeted pseudotetrahedral species were not isolated. The Tpm* ligand exhibited a marked propensity
to support octahedral nickel(II) complexes arising from multiple ligand additions, further abetted by the presence of
protons or water. Product complexes obtained from the reagents just enumerated included [Tpm*NiII(OH2)(3-
ClC6H4CO2)2] (2), [(Tpm*)2NiII][NiII(NHTs)4] (3), and [Tpm*NiII(OH)2(OH2)] (4), respectively. The syntheses and
characterizations of these are described herein, which adds to the small extant body of nickel-tris(pyrazolyl)methane
coordination chemistry [12, 24-32].
2.0 Materials and Methods
2.1 General procedures.
All materials obtained from commercial vendors were ACS reagent-grade or better and used as received,
except for drying of solvents by routine techniques. The Tpm* ligand [33], phenyl-N-tosyliminoiodinane (PhINTs)
[34], and 2-(tert-butylsulfonyl)iodosylbenzene (ArIO) [35] were prepared by literature procedures. All
manipulations were carried out under an inert atmosphere of prepurified argon, either in a glovebox (MBraun
Unilab) or using Schlenk techniques. 1H NMR data were recorded on a Varian Unity 500 spectrometer and
processed using the MestReNova 5.1 software suite (Mestrelab Research, Santiago de Compostela, Spain); spectra
were referenced internally to the residual solvent resonance(s). UV-visible-NIR spectra were recorded on an
Agilent HP-8453 diode-array spectrophotometer. Elemental analyses were performed by Atlantic Microlabs, Inc.
(Norcross, GA).

3
2.2 Preparation of [Tpm*NiII(OH2)Cl2] (1) [32].
Anhydrous NiCl2 (195 mg, 1.50 mmol) dissolved in MeOH (15 mL) was added to a solution of Tpm* (450
mg, 1.51 mmol) in CH2Cl2 (20 mL). After brief stirring, removal of solvent under vacuum gave 1 as a green
microcrystalline powder, which was recrystallized by slow evaporation of a CH3CN solution under air. Yield: 590
mg (1.32 mmol, 88%). Anal. Calc’d. (Found) for C16H25Cl2N6NiO1.5, 1•0.5H2O: C, 42.23 (42.15); H, 5.54 (5.57);
1
1
N, 18.47 (18.53). H NMR (CD3CN, 295 K, δ ppm): 51.8 (3H, 4-H); -2.6 (9H, 5-Me); -8.7 (10H, 3-Me + CH). H
NMR (D2O, 295 K, δ ppm): 54.6 (3H, 4-H); -2.3 (9H, 5-Me); -8.0 (1H, CH); -10.1 (9H, 3-Me).
2.3 Preparation of [Tpm*NiII(OH2)(3-ClC6H4CO2)2] (2).
A 1:1 mixture of m-chloroperoxybenzoic acid (51.8 mg, 0.30 mmol) and m-chlorobenzoic acid (47.0 mg,
0.30 mmol) were dissolved together in THF (10 mL) and slowly added to a solution of [Ni0(COD)2] (82.5 mg, 0.30
mmol) and Tpm* (90.0 mg, 0.30 mmol) together in THF (15 mL). The combined solutions turned light green. The
solvent was stripped and the residue was washed with Et2O. Green crystals of 2•CH2Cl2•0.5C6H14 were obtained by
dissolving the remaining solids in CH2Cl2 and layering with hexanes. Yield: 106 mg (0.13 mmol, 43% yield).
Anal. Calc’d. (Found) for C30H32Cl2N6NiO5, 2: C, 52.51 (53.22); H, 4.70 (4.63); N, 12.25 (11.79). 1H NMR
(CD3CN, 295 K, δ ppm): 44.6 (3H, 4-H); 13.9 (2H, mcba); 10.9 (2H, mcba); 9.9 (2H, mcba); 7.6 (2H, mcba); -1.2
1
(9H, 5-Me); -5.6 (1H, CH); -11.9 ppm (9H, 3-Me). H NMR (CD2Cl2, 295 K, δ ppm): 45.8 (3H, 4-H, species b);
43.6 (3H, 4-H, species a); 12.8 (2H, mcba, a); 10.9 (2H, mcba, a); 10.1 (sh, 2H, mcba, a); 9.5 (2H, mcba, b); 8.79
(4H, mcba, b); 7.9 (2H, mcba, a); 7.6 (2H, mcba, b); -1.3 (9H, 5-Me, a); -2.2 (9H, 5-Me, b); -5.5 (1H, CH, a); -6.4
(1H, CH, b); -8.9 ppm (9H+9H, 3-Me, a+b).
2.4 Preparation of [(Tpm*)2NiII][NiII(NHTs)4] (3).
A 1:1 mixture of [Ni0(COD)2] (110 mg, 0.39 mmol) and Tpm* (120.0 mg, 0.40 mmol) were dissolved
together in THF (15 mL) and added slowly to a suspension of PhINTs (187 mg, 0.50 mmol) in THF (15 mL) at
room temperature. The PhINTs eventually dissolved and the solution turned purple. After stirring 20 m, a brown

4
precipitate began to appear. After stirring 4 h, solvent was removed under vacuum. The purple-brown solid was
extracted into CH2Cl2 (3 mL). The extracts were filtered, layered with diethyl ether and allowed to stand at -37 °C.
Purple crystals of 3 were isolated by filtration. Yield: 115 mg (0.08 mmol, 42 %). Anal. Calc’d. (Found) for
1
C60H80N16Ni2O10S4, 3•2H2O: C, 50.36 (50.53); H, 5.63 (5.55); N, 15.66 (15.48). H NMR (CD3CN, 295 K, δ ppm):
54.4 (6H, 4-H); 10.4 (8H, Ts); 8.8 (8H, Ts); 3.7 (12H, Ts); -2.8 (18H, 5-Me); -9.8 (18 H, 3-Me); -13.9 (2H, CH), -
99.4 (4H, NHTs).
2.5 Preparation of [Tpm*NiII(OH)2(OH2)] (4).
A 1:1 mixture of [Ni0(COD)2] (110 mg, 0.40 mmol) and Tpm* (120 mg, 0.40 mmol) were dissolved
together in THF (15 mL) and slowly added to a suspension of 2-(tert-butylsulfonyl)iodosylbenzene (153mg, 0.45
mmol) in THF (2 mL) at room temperature. The resulting pale yellow-green solution was allowed to stir at room
temperature for 4 hours. Solvent was then stripped and the pale yellow-green solid was dissolved in a minimal
amount of CH2Cl2 and layered with n-hexane. The sample was kept at -37 ºC until light purple crystals of 4•CH2Cl2
formed. Yield: 89 mg (0.18 mmol, 45%). Anal. Calc’d. (Found) for C17H28Cl2N6NiO3, 4•CH2Cl2: C, 41.33
1
(41.92); H, 5.71 (4.92); N, 17.01 (16.90). H NMR (CD3CN, 295 K, δ ppm): 54.3 (3H, 4-H); -2.8 (9H, 5-Me); -9.7
(10H, 3-Me+CH).
2.6 X-ray Crystallography.
X-ray crystal structures were determined for complexes 1-3. Crystal and refinement information are
summarized in Table 1; thermal ellipsoid plots are shown in Figures 1, 3 and 6 with relevant bond lengths and
angles listed in each caption. Unusual details of the structure solution and refinement for each complex are
summarized below.
The asymmetric unit of [{HC(C5H7N2)3}NiCl2(H2O)] (1) contained two independent molecules. Hydrogen
atoms on the coordinated waters were refined isotropically with the O-H bond distances restrained to 0.85 0.02 Å.
The lattice of [{HC(C5H7N2)3}Ni(C7H4ClO2)2(H2O)]•CH2Cl2•0.5C6H14 (2•CH2Cl2•0.5C6H14) contained one
dichloromethane per asymmetric unit, which was ordered. Compositional disorder of at least two structural isomers

5
of hexane was evident on a crystallographic inversion center; it appeared that n-hexane filled this site most of the
time, but 2-methyl-pentane was present as a substantial fraction. The disordered solvent was removed by applying
Platon/Squeeze [36]. The solvent filled 199.6 Å3, or 10.54% of the unit cell volume. 51 electrons were found
within this space, corresponding approximately to one “hexanes” molecule per unit cell. The R1 value improved
from ~0.08 to 0.0495 following the application of Platon/Squeeze and several cycles of least-squares refinement.
The librational motion of the meta-chloro-benzoate group appears to be an artifact of the solvent disorder.
A violet crystal of [{HC(C5H7N2)3}2Ni][Ni(NH{SO2C6H4-4-CH3})4]•2MeCN (3•2MeCN) was obtained on
standing from a CD3CN solution. Both nickel atoms were found on different crystallographic inversion centers.
One molecule of acetonitrile was found in a general position. The NHTs ligands form a ring of four hydrogen
bonds; the two unique hydrogen atoms were allowed to refine positionally with a common distance restraint.
3.0 Results and Discussion
3.1 General remarks.
X-ray structures were previously reported for the sandwich dication [(Tpm*)2NiII]2+ (Tpm*, tris{3,5-
dimethylpyrazol-1-yl)}methane) as the bis(tetrafluoroborate) [26], dibromide [27], and (NiCl4)2- salts [28], as well
as the half-sandwich complex [Tpm*NiII(κ2-NO3)(κ1-NO3)] [29].
Another half-sandwich complex
[(Tpm*)NiII(OH2)Cl2] (1) was previously reported [32], but its structure was not determined. Therefore, we repeated
the synthesis of 1 and obtained its structure (Figure 1) for the purpose of comparison to analogous products obtained
herein (vide infra).
3.2 Characterization of [Tpm*NiII(OH2)Cl2] (1)
The structure of 1 consists of two independent molecules of [Tpm*NiII(OH2)Cl2] connected by
intermolecular Cl•••HO conntacts inn the range of 2.32(3)-2.52(3) Å, shorter than the sum of van der Waals radii. The
metal-ligand bond lengths are consistent with a d8 electron configuration (3A2g under ideal octahedral symmetry) in
which both dσ* (i.e., eg) orbitals are singly occupied. The Ni-N bonds fall in a narrow range of 2.088(2)-2.167(2) Å;

6
the nitrogen situated trans to the aquo ligand exhibits a slightly shorter average bond length, 2.10(1) Å than the
nitrogens trans to the chlorides, 2.15(1) Å. The overall average Ni-N bond length of 2.13(3) Å can be compared to
an averaged value of 2.10(1) Å in various salts of [(Tpm*)2NiII]2+ [26-28], and a range of 2.010(3)-2.135(3) Å in
[Tpm*NiII(κ1-NO3)(κ2-NO3)] [29]. The Ni-OH2 and Ni-Cl bond lengths average 2.09(1) and 2.41(1) Å, respectively.
To further describe the structure of 1, a plane is defined to include both chlorides and the two trans
pyrazole nitrogens (i.e., N3, N5 on Ni1 and N9, N11 on Ni2). The nickel atoms reside within 0.015 Å of the least-
squares mean in both independent molecules. Within this “square” plane, the cis Cl-Ni-Cl bond angles are slightly
opened, 93.16(2)° (Ni1) and 94.91(3)° (Ni2), while the N-Ni-N bond angles, constrained by the bite of the Tpm*
chelate, are 83.06(8)° (at both Ni1 and Ni2). The cis Cl-Ni-N angles fall in a range of 90.11(6)°-92.64(6)°; thus, the
cis bond angles within the N2NiCl2 plane sum to an average value of 359(1)°. The trans N-Ni-Cl angles range from
173.07(6)°-174.99(6)°. The aquo ligand is essentially orthogonal to this plane, with two cis O-Ni-N angles and two
cis O-Ni-Cl angles ranging from 88.64(8)°-91.71(5)° with an average value of 90(1)°. However, the trans pyrazole
nitrogen is constrained from optimal octahedral coordination by the ligand bite; the trans N-Ni-OH2 angle is non-
linear, 172.29(8)° (N1-Ni1-O1) and 173.67(8)° (N7-Ni2-O7), and bent away from the chlorides. The cis N-Ni-N
and N-Ni-Cl bond angles range from 84.50(8)°-85.80(8)° and 93.44(6)°-96.42(6)°, respectively. Overall, six cis N-
Ni-N angles on both Tpm* ligand complexes are constrained to a range of 83.06(8)-85.80(8)°. This contrasts with
the anionic boron-collared Tp* ligand, which supports numerous 4- and 5-coordinate Ni(II) complexes with cis N-
Ni-N angles in excess of 90° [11]. The higher coordination number favored by the Tpm* ligand presumably results
from its neutral charge and constrained bite. This conclusion impacted our synthetic strategy of oxidizing
[Ni0(COD)2] in the presence of Tpm* with disparate oxene and nitrene transfer reagents, which resulted in formation
of a different octahedral Tpm*-supported Ni(II) product complex in each case.
3.3 Addition of Tpm* to [Ni0(COD)2]
1
A 1:1 mixture of [Ni0(COD)2] and Tpm* dissolved in d8-THF was examined by H NMR spectroscopy at
room temperature (Figure 2). Observed resonances were assigned to intact [Ni0(COD)2], free Tpm* and free COD.
While partial solvation of [Ni0(COD)2] was observed, no interaction with Tpm* was evident. A similar result was
observed in a previous study for addition of Tpm to [Ni0(COD)2], used to promote cross-coupling of aryl halides:

7
Tpm was proposed to interact only with nickel(II) generated by oxidative addition [37]. We pursued a parallel
strategy of adding mcbpa, PhINTs or ArIO to the [Ni0(COD)2]/Tpm* mixture.
3.4 Synthesis and characterization of [Tpm*NiII(OH2)(3-ClC6H4CO2)2] (2).
Addition of pure mcpba to the d8-THF solution of [Ni0(COD)2]/Tpm* generated multiple paramagnetic
species as observed by 1H NMR spectroscopy. Co-addition of m-chlorobenzoic acid (mcba) gave cleaner conversion
to [Tpm*NiII(OH2)(3-ClC6H4CO2)2] (2).
We expected that peroxidation of [Ni0(COD)2] would form
[Tpm*NiII(OH)(3-ClC6H4CO2)] by oxidative addition (eqn. 1), with subsequent capture of the carboxylic acid
impurity giving rise to 2 (eqn. 2). However, a reduced yield of 2 was obtained by adding mcba alone; hence, proton
reduction by Ni(0) must be competitive [38], leading to 2 by capture of carboxylate anions and H2O (eqns. 3, 4).
LNiII(OH)(O2CR)
LNiII(OH2)(O2CR)2
LNiII(O2CR)2 + H2
LNiII(OH2)(O2CR)2
L+ Ni0 + RC(O)OOH
LNiII(OH)(O2CR) + RCO2H
L+ Ni0 + 2 RC(O)OH
LNiII(O2CR)2 + H2O
[1]
[2]
[3]
[4]
The structure of 2 determined by X-ray crystallography (Figure 3) is analogous to that of 1, with κ1-
carboxylato ligands in place of the chlorides. The Ni-OH2 bond length in 2, 2.080(2) Å is similar to that of 1, as are
the Ni-N bond lengths, which range from 2.099(2)-2.153(2) Å. The Ni-N bond trans to the aquo ligand is slightly
shorter than the two Ni-N bonds disposed trans to the anionic carboxylates. The Ni-OC(O)R bond lengths are
2.046(2) (Ni1-O1) and 2.064(2) Å (Ni1-O3). The cis N-Ni-N angles average 85(2)° in 2, compared to 84(1)° in 1.
As in the structural analysis of 1, a least-squares plane can be defined by the carboxylate oxygens and trans
nitrogens (N2, N6, O1, and O3). However, the nickel atom in 2 is displaced 0.104 Å out of this plane, towards the
aquo ligand (O5) and away from the trans pyrazole (N4). Also unlike 1, the trans N4-Ni1-O5 angle to the aquo
ligand is nearly linear, 179.30(8)°, while the trans N-Ni-O angles to the carboxylates are bent, 171.78° (N2-Ni1-O3)
and 173.19(8)° (N6-Ni1-O1). Again unable to fully span an octahedral face, the Tpm* ligand is displaced onto the
N4-Ni1-OH2 axis in 2, rather than into the orthogonal N2O2 plane, as in 1. This difference may reflect disparate
hydrogen bonding of the aquo ligands. While 1 exhibits intermolecular Cl•••HO contacts, the carboxylato ligands of

8
2 support short intramolecular hydrogen bonds between the unligated oxygens and the aquo protons, 1.82(3) Å
(H5D•••O2) and 1.84(3) Å (H5E•••O4).
1H NMR spectra of 1 and 2 in CD3CN solution are consistent with paramagnetic (S = 1) electron
configurations resulting from octahedral coordination of d8 nickel(II). The spectrum of 1 exhibits three signals in a
3:9:10 intensity ratio at 51.8, -2.6 and -8.7 ppm, respectively assigned to the 4-H, 5-Me, and 3-Me pyrazolyl
resonances respectively, with the latter overlapping the methine signal (Figure 4A). The spectrum of 2 contains
analogous Tpm* ligand resonances at 44.6, -1.2 and -11.9 ppm, with a resolved methine resonance at -5.6 ppm; four
additional resonances at 13.9, 10.9, 9.9, and 7.6 ppm are assigned to the m-chlorophenyl substituents of the
carboxylate ligands (Figure 4B). The slight paramagnetic shifts indicate the carboxylates remain coordinated to
nickel(II), and the relative broadness of the two middle resonances is consistent with assignment to the inequivalent
ortho protons. Unlike 1, complex 2 is soluble in less polar solvents such as CD2Cl2, in which the spectrum exhibits a
second , somewhat broader set of resonances (labeled “b” in Figure 4C). This second species is assigned as the
intact complex [Tpm*NiII(OH2)(3-ClC6H4CO2)2,], while the species observed in CH3CN may result from solvation of
the aquo ligand, resulting in a dehydrated [Tpm*NiII(3-ClC6H4CO2)2] derivative with at least one κ2-carboxylato
ligand.
Both 1 and 2 exhibit solution-phase UV-Vis spectra consistent with octahedral coordination of a d8 Ni(II)
ion (Figure 5) [30]. The spectrum of 1 in MeOH is very similar to the previously reported aqueous spectrum
(wherein solvolysis of the chlorides is expected) [32], with spin-allowed bands at 996 nm (3T2{F} • 3A2) and 624 nm
3
3
(3T1{F} • A2) and a spin forbidden band (1E • A2) appearing as a weak shoulder at 741 nm. Alignment on the
3
Tanabe-Sugano diagram gives ∆O = 10,000 cm-1, B = 880 cm-1, and places the third spin-allowed (3T1{P} • A2)
transition at 360 nm, where it is obscured by the tail of strong UV bands. The spectrum of 2 in non-polar CH2Cl2 is
modestly red-shifted, consistent with its neutral charge and the spectrochemical series (ROH > RCO2-), while a UV
shoulder with partially resolved fine structure reflects the presence of the aromatic substituents on the carboxylato
ligands.
3.5 Synthesis and characterization of [(Tpm*)2NiII][NiII(NHTs)4] (3).

9
Oxidation of [Ni0(COD)2]/Tpm* with a suspension of the nitrene precursor PhINTs in THF gave a dark
violet homogeneous solution that yielded a brown precipitate on standing. This product was recrystallized and
identified as [(Tpm*)2NiII][NiII(NHTs)4] (3). Proton reduction by [Ni(COD)2] is discounted in this reaction, since the
1
PhINTs reagent dissolved and a control mixture of 1:1:1 [Ni0(COD)2]:Tpm*:TsNH2 monitored in d8-THF by H
NMR spectroscopy gave no evidence of reactivity. Instead, the initial reaction of [Ni0(COD)2] and PhINTs may
produce the intended imido complex product, namely pseudotetrahedral [Tpm*NiIINTs] (eqn. 5). However,
subsequent addition of free tosylamine, liberated by hydrolysis of PhINTs, would form the neutral bis(amido)
complex [(TpmNiII(NHTs)2], a coordination isomer of the observed product salt (eqns. 6-8).
L+ Ni0 + PhINTs
PhINTs + H2O
LNiII(NTs) + PhI
PhIO + TsNH2
LNiII(NHTs)2
[5]
[6]
LNiII(NTs) + TsNH2
[7]
[8]
II
II
2 LNi (NHTs)2
[L2NiII][Ni (NHTs)4]
The structure of the [(Tpm*)2NiII]2+ dication determined by X-ray crystallography is unremarkable (Figure
6). The pseudo-octahedral (ideally D3d) nickel atom sits on an inversion center, so only half of the sandwich
structure is unique. The average Ni-N bond length is 2.106(6) Å and the intra- and inter-ligand cis N-Ni-N bond
angles are 85.3(6)° and 94.7(6)°, respectively, equivalent to three previous structures with different counterions [26-
28]. In constrast, the square-planar [NiII(HNTs)4]2- dianion is rather unique. A large number of Ni(II) complexes
with N-substituted sulfonamidato donors have been reported, but these are typically incorporated into chelating
ligands [39-41]; only two previous examples feature primary monodentate [HNS(O)2R]- anions, and these were
neutral octahedra [42,43]. The nickel atom sits on a separate inversion center. The two unique Ni-N bond lengths
are effectively equivalent, 1.922(2) Å (Ni2-N7) and 1.921(2) Å (Ni2-N8), and the cis N-Ni-N bond angles are nearly
square, 92.09(6)° (N7-Ni2-N8) and 87.91(6)° (N7-Ni2-N8•). The tosyl substituents also support a unique collar of
N-H•••O=S hydrogen bonds around the NiN4 plane, 2.11(2) (O2•••H8A) and 2.13(2) Å (O3•••H7B).
The product salt 3 was soluble only in polar solvents. Notwithstanding the square-planar structure
1
observed in the solid state, a solution H NMR spectrum was also consistent paramagnetism of the dianion in
CD3CN. The tosyl resonances (labeled “c” in Figure 4D) were shifted slightly downfield (10.4, 8.8 and 3.7 ppm),
while a pronounced upfield peak (at -99.4 ppm) was tentatively assigned to the amide protons. Observed

10
paramagnetic shifts of resonances for the [(Tpm*)2NiII]2+ dication in CD3CN solution were consistent with a previous
report [27]. The UV-Vis-NIR spectrum in CH3CN (Figure 5) appeared to be consistent with a superposition of two
octahedral species, presumably reflecting solvent coordination to the dianion. Similar to a previous report [30], the
3
lowest-energy ligand field transition (3T2{F} • A2) of the dication [(Tpm*)2NiII]2+ was observed at 869 nm (11,500
cm-1), while the split band centered roughly at 560 nm (17,900 cm-1) was assigned to the second ligand field band
(3T1(F) • 3A2). A second set of bands arising from the dianion was evident, with a slight blue shift to 759 nm (13,200
cm-1) and 442 nm (22,700 cm-1); the latter appeared to be split, overlapping the higher energy peak of the dication as
a shoulder.
3.6 Synthesis and characterization of [Tpm*NiII(OH2)(OH)2] (4).
No reaction was obtained from addition of insoluble PhIO to a 1:1 mixture of [Ni0(COD)2]/Tpm* in THF.
t
However, the substituted analog 2-BuSO2C6H4IO readily dissolved and oxidized the [Ni0(COD)2] in the presence of
Tpm*. A 1H NMR spectrum of the crude reaction mixture extracted into CDCl3 (Figure 4E) revealed the presence of
free COD and the reduced aryl iodide. A major paramagnetic species was observed that exhibited resonances similar
to the other octahedral complexes already described (Figure 4A-C), indicating that Tpm* was bound to nickel(II) in
a half-sandwich complex. Elemental analysis of pale purple crystals isolated from the reaction mixture indicated a
molecular mass of 498(1) amu, extrapolated from the nitrogen analysis and normalized to the six atoms of the Tpm*
ligand. The excess mass beyond the target complex [Tpm*Ni(O)] (373 amu) was tentatively ascribed to addition of
two H2O molecules (eqns. 9-11) and
a
lattice CH2Cl2 molecule, giving
a
formulation
of
[Tpm*NiII(OH2)(OH)2]•CH2Cl2 (4•CH2Cl2, 494 amu). Since 4 appears to be an octahedral complex analogous to 1 or
2, further structural characterization of this product was not pursued.
LNiII(O) + ArI
LNiII(OH)2
L+ Ni0 + ArIO
LNiII(O) + H2O
[9]
[10]
[11]
LNiII(OH2)(OH)2
LNiII(OH)2 + H2O
4.0 Conclusions

11
The goal of this work was synthesis of hypothetical pseudotetrahedral species [Tpm*NiII=E] (E = O, NTs),
1
by oxene atom or nitrene group transfer to [Tpm*Ni0(COD)]. H NMR spectroscopy of a d8-THF reaction solution
clearly establishes that neutral Tpm* does not add to partial solvated [Ni0(COD)2]. Addition of mcpba, PhINTs or
ArIO results in two-electron oxidation and assembly of Tpm*NiII complexes, but the reactivity does not yield the
desired pseudotetrahedral products. Instead, the Tpm* ligand exhibited a marked propensity to favor octahedral
nickel(II), which seems to arise from a relatively constrained bite. This abetted further addition of fragments
derived from the oxidizing precursors, either carboxylic acid, tosylamine, or H2O. The presence of acidic reagents or
trace water, presumably within the hypervalent iodonium ylides, further exacerbated the lability of Tpm* and the
various co-ligands on Ni(II). Nevertheless, the obtained pseudo-octahedral Tpm* complexes, [Tpm*NiII(OH2)(3-
ClC6H4CO2)2] (2) and [Tpm*NiII(OH)2(OH2)] (4) add to the scope of nickel-tris(pyrazolyl)methane coordination
chemistry. The tetraamido complex dianion [NiII(NHTs)4] present in 3 is also rather unique. Finally, there is
evidence that the desired oxidative oxene and nitrene transfer chemistry may occur from hypervalent iodonium
ylides. Thus, it will be worth exploring in future work whether substitution of other oxidative substrates under dry
conditions and modification of the supporting scorpionate ligand, with either enhanced steric bulk or an anionic
hydroborato linker, might enable isolation of pseudotetrahedral oxo and imido complexes as kinetic products of this
reactivity.
Acknowledgments. The authors acknowledge the donors of the American Chemical Society Petroleum Research
Fund (49296-DNI3) for support of this work. SL thanks the Condensed Matter and Surface Science (CMSS)
Program at Ohio University for a graduate research fellowship.
Appendix A. Supplementary data. CCDC 878076-878078 contain crystallographic data for compounds 1-3.
These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk.

12
Table 1. Summary of X-ray crystallography.
Compound
[Tpm*Ni(OH2)Cl2] (1)
[Tpm*Ni(OH2)(O2CC6H4-3-Cl)2]
•CH2Cl2•0.5C6H14 (2)
C34H41Cl4N6NiO5
814.24
173(2)
Triclinic
[(Tpm*)2Ni][Ni(NHTs)4]
•2CH3CN (3)
C64H82N18Ni2O8S4
1477.14
123(2)
Monoclinic
P21/n
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C16H24Cl2N6NiO
446.02
293(2)
Orthorhombic
Pbca
P-1
a (Å)
b (Å)
c (Å)
α (deg)
15.8781(9)
13.9478(8)
35.968(2)
90
10.169(1)
12.248(1)
15.680(2)
98.767(2)
11.973(1)
18.591(2)
15.736(2)
90
90
90
7965.6(8)
16
91.705(2)
100.682(2)
1893.3(4)
101.162(1)
90
3436.3(6)
2
β (deg)
γ (deg)
V (Å3)
Z
2
Density (calc, g/cm3)
Absorption coefficient (mm-1)
Crystal color, morphology
Crystal size (mm)
Reflections collected
Independent reflections (Rint)
Observed reflections
Data/restraints/parameters
GoF
1.488
1.260
1.428
0.843
1.428
0.737
Colorless, block
0.10 x 0.24 x 0.40
52862
9092 (0.0593)
7035
Blue, block
0.45 x 0.18 x 0.15
21539
8523 (0.0309)
6692
Violet, plate
0.50 x 0.50 x 0.15
40943
7871 (0.0319)
6558
9092/4/497
1.025
8523/2/436
1.084
7871/1/451
1.066
0.0405, 0.0997
0.0574, 0.1110
0.620, -0.436
0.0495, 0.1262
0.0649, 0.1341
1.840, -1.886
0.0315, 0.0790
0.0431, 0.0873
0.520, -0.370
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
Difference peak, hole (e/ Å3)

13
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16
Highlights:
• Tris(3,5-dimethylpyrazol-1-yl) complexes of nickel. • Oxidation of Ni(COD)2 • In situ assembly of octahedral
scorpionate nickel(II) complexes • Spectroscopic and structural characterizations
Key words:
Tris(pyrazolyl)methane
Nickel
Amido ligand
Hydrogen bonding
meta-Chloroperoxybenzoic acid
Iminoiodinane
Iodosylbenzenes
Figure Captions
Figure 1. Thermal ellipsoid plot of 1 (50% ellipsoids). Bond lengths (Å): Ni1-N1, 2.088(2); Ni1-N3, 2.147(2);
Ni1-N5, 2.167(2); Ni1-Cl1, 2.426(1); Ni1-C12, 2.420(1); Ni1-O1, 2.078(2); C11•••H2aa, 2.316;; CC12•••H2bb, 2.518;
Ni2-N7, 2.108(2); Ni2-N9, 2.136(2); Ni2-N11, 2.159(2); Ni2-Cl3, 2.400(1); Ni2-Cl4, 2.408(1); Ni2-O2, 2.093(2);
C13•••H1a, 2..410;; C14•••••H1b,, 2.4226. Bond anngles ((°): NN1-Ni1-N3, 84.50(8); N1-Ni1-N5, 85.80(8); N1-Ni1-Cl1,
94.28(6); N1-Ni1-Cl2, 96.42(6); N3-Ni1-N5, 83.06(8); N3-Ni1-O1, 89.54(8); N3-Ni1-Cl2, 92.64(6); N5-Ni1-O1,
88.64(8); N5-Ni1-Cl1, 91.17(6); O1-Ni1-Cl1, 91.17(6); O1-Ni1-Cl2, 88.71(6); Cl1-Ni1-Cl2, 93.16(2); N1-Ni1-O1,
172.29(8); N3-Ni1-Cl1, 174.17(6); N5-Ni1-Cl2, 174.97(6); N7-Ni2-N9, 84.87(8); N7-Ni2-N11, 85.49(8); N7-Ni2-
Cl3, 93.44(6); N7-Ni2-Cl4, 94.29(6); N9-Ni2-N11, 83.06(8); N9-Ni2-O2, 89.58(7); N9-Ni2-Cl4, 91.93(6); N11-
Ni2-O2, 90.84(8); N11-Ni2-Cl3, 90.11(6); O2-Ni2-Cl3, 91.71(5); O2-Ni2-Cl4, 88.92(6); Cl3-Ni2-Cl4, 94.91(3);
N7-Ni2-O2, 173.67(8); N9-Ni2-Cl3, 173.07(6); N11-Ni2-Cl4, 174.99(6).
Figure 2. 1H NMR spectra (d8-THF, 295 K): (A), 1:1 Tpm* and [Ni0(COD)2]; (B), free Tpm*; (C), free COD.
Peaks due to residual solvent are marked “s”.
Figure 3. Thermal ellipsoid plot of 2 (50% probability). Bond lengths (Å): Ni1-N2, 2.129(2); Ni1-N4, 2.099(2);
Ni1-N6, 2.153(2); Ni1-O1, 2.046(2); Ni1-O3, 2.064(2); Ni1-O5, 2.080(2); O2··H5d, 1.823; O4··H5e, 1.838. Bond
angles (°): N2-Ni1-N4, 84.25(8); N2-Ni1-N6, 83.75(8); N2-Ni1-O1, 90.36(8); N2-Ni1-O5, 96.44(8); N4-Ni1-N6,
87.18(8); N4-Ni1-O1, 88.83(8); N4-Ni1-O3, 88.16(8); N6-Ni1-O3, 92.75(8); N6-Ni1-O5, 92.72(8); O1-Ni1-O3,
92.63(8); O1-Ni1-O5, 91.33(8); O3-Ni1-O5, 91.15(7); N2-Ni1-O3, 171.78(8); N4-Ni1-O5, 179.30(8); N6-Ni1-O1,
173.19(8).
Figure 4. 1H NMR spectra (295 K): (A), solvated 1 in wet CD3CN; (B), 2 in CD3CN; (C), 2 in CD2Cl2; (D), 3 in
CD3CN; (E), crude products including 4 from reaction of 1:1:1 [Ni0(COD)2]:Tpm:2-tBuSO2C6H4IO in THF,
extracted into CDCl3. Peaks due to residual solvent are marked “s”; lattice solvents (CH2Cl2, hexane) are denoted
with an asterisk (*). In (A) and (E), tall peaks are truncated (~) for clarity. In (A), pyrazole resonances of 1 are
labeled by position. In (C), two independent sets of resonances for 2 are labeled (a, b). In (D), resonances of tosyl
t
substituents of 3 are labeled (c). In (E), resonances of BuSO2C6H4I and free COD are labeled (d) and (e),
respectively.
Figure 5. UV-Vis-NIR spectra (295 K) of solvated 1 in CH3OH (solid line), 2 in CH2Cl2 (dashed line, ---) and 3 in
CH3CN (dotted line, •••).
Figure 6. Thermal ellipsoid plot of 3 (50% probability). Hydrogen atoms omitted for clarity, except for amides.
Bond lengths (Å): Ni1-N2, 2.102(2); Ni1-N4, 2.113(1); Ni1-N6, 2.102(1); Ni2-N7, 1.922(2); Ni2-N8, 1.921(2);
O2•••H8A, 2.11(2); O3•••H7B, 2.13(2). Bond angles (°): N2-Ni1-N4, 85.37(5); N2-Ni1-N6, 85.94(6); N4-Ni1-N6,
84.65(5); N2-Ni1-N2′, 180; N2-Ni1-N4′, 94.63(5); N2-Ni1-N6′, 94.06(6); N4-Ni1-N4', 180; N4-Ni1-N6′, 95.35(5);
N6-Ni1-N6′, 180; N7-Ni2-N8, 92.09(6); N7-Ni2-N8′, 87.91(6); N7-Ni2-N7′, 180; N8-Ni2-N8′, 180.

Cl2
N9
N1
O2
Ni1
Cl1
N11
N3
Cl4
Ni2
N7
O1
N5
Cl3

(C)
s
s
(B)
(A)
10
9
8
7
6
5
4
3
2
1
0
 (ppm)

O2
O4
O5
O3
O1
Ni1
N4
N2
N6

e
~
e
d
~~
s
d
(E)
(D)
c
s
c
c
*
*
b
s
b
a
(C)
(B)
a+b
b
a
a
b
a
b
*
*
s
*
*
s
~
5
(A)
3
4
60
55
50
45
15
10
5
0
-5
-10
-15
 (ppm)

60
50
40
30
20
10
0
400
500
600
700
800
900
1000
 (nm)

N2
N6
N7
Ni2
N8
Ni1
N6
N8
N2
N7

17
Table of Contents
Oxidation of Ni(COD)2 with a variety of oxene and nitrene precursors in the presence of tris(3,5-dimethylpyrazol-1-
yl)methane (Tpm*) leads to isolation of several octahedral Tpm*-supported nickel(II) complexes.