Synthesis and characterization of [Ga(TPP)H] (TPP = tetraphenylporphyrinato)

Article abstract of DOI:10.1016/S1387-7003(03)00014-5

The synthesis, spectroscopic and structural characterization of the stable gallium hydride compound [Ga(TPP)H] (TPP = 5,10,15,20-tetraphenylporphyrinato) have been reported. The hydride compound was synthesized in high yield (85%) by reducing [Ga(TPP)Cl] with sodium borohydride in N,N-dimethylformamide. The title compound was fully characterized by spectroscopic methods (IR, UV-Vis, and ¹H NMR spectroscopy) and its molecular structure was established by X-ray crystallography. The Ga-H IR stretch occurs at 1864 cm^-1, and the hydride ¹H NMR resonance locates at -6.47 ppm. The gallium-hydrogen distance is 1.48(4) ?, whereas the gallium atom lies 0.46(1) ? from the perfect porphyrin plane.

Full text of DOI:10.1016/S1387-7003(03)00014-5

Inorganic Chemistry Communications 6 (2003) 466–468
www.elsevier.com/locate/inoche
Synthesis and characterization of
[Ga(TPP)H] (TPP ¼ tetraphenylporphyrinato)
*
Yaoyu Feng , Say-Leong Ong, Jiangyong Hu, Wun-Jern Ng
Department of Civil Engineering, National University of Singapore, Singapore 119260, Singapore
Received 18 October 2002; accepted 23 December 2002
Abstract
The synthesis, spectroscopic and structural characterization of the stable gallium hydride compound [Ga(TPP)H]
(TPP ¼ 5,10,15,20-tetraphenylporphyrinato) have been reported. The hydride compound was synthesized in high yield (85%) by
reducing [Ga(TPP)Cl] with sodium borohydride in N; N-dimethylformamide. The title compound was fully characterized by
spectroscopic methods (IR, UV–Vis, and 1H NMR spectroscopy) and its molecular structure was established by X-ray crystal-
lography. The Ga–H IR stretch occurs at 1864 cmÀ1, and the hydride 1H NMR resonance locates at )6.47 ppm. The gallium–
ꢀ
ꢀ
hydrogen distance is 1.48(4) A, whereas the gallium atom lies 0.46(1) A from the perfect porphyrin plane.
Ó 2003 Elsevier Science B.V. All rights reserved.
Keywords: Gallium; Porphyrin; Hydride; Crystal structure
1. Introduction
has the potential to act as the precursor for a series of r-
bonded alkyl and aryl porphyrins, bi-or trimetallic
metal–metal-bonded metalloporphyrins due to the
weakness and reactivity of the Ga–H bond.
The chemistry of gallium hydrides has attracted ex-
tensive interest due to their potential application in areas
ranging from organic synthesis (serving as precursors to
solid-state materials such as gallium nitride, and as re-
ducing agents etc.) to chemical vapor deposition [1].
Stable gallium hydride compounds are usually obtained
in the form of Lewis acid–base adducts, H3Ga(base) [2–
4]. There are also a significant number of other struc-
turally characterized alkyl gallium monohydrides and
dihydrides that are most often formed using LiGaH4 or
GaH3 [5–9]. Recent work has shown that it is possible to
use bulky aryl groups to synthesize Group 13 hydride
species [10–12].
In this paper we used the macrocyclic ligand tetra-
phenylporphyrin as the coordinating reagent to stabilize
the gallium hydride compound. Similarly, rhodium
porphyrin hydride compounds have been reported and
extensively used in chemical synthesis and catalysis [13–
15]. The obtained hydride compound [Ga(TPP)H] (1) is
considerably stable at ambient environment and thus
2. Experimental
2.1. Synthesis
To a solution of Ga(TPP)Cl [16] (200 mg, 0.28 mmol)
in N; N-dimethylformamide (DMF) (100 ml), sodium
borohydride (30 mg, 0.79 mmol) was added. With the
addition of sodium borohydride, the color of the solu-
tion changed from red to green gradually and green
precipitate was formed in the reaction mixture. The re-
action system was vigorously stirred at room tempera-
ture for 1 h, then the resulting reaction mixture was
filtered and the green crystalline 1 was obtained (160 mg,
yield: 85%) after thoroughly washed with distilled water
and methanol. Elemental analysis found (calcd. based
on C44H29GaN4): C 77.04 (77.32); H 4.42 (4.28); N 8.01
(8.20). IR (KBr pellet, cmÀ1) m: 1864(m), 1596(m),
1513(w), 1487(m), 1440(m), 1342(m), 1206(m), 1175(m),
1071(m), 1003(vs), 803(s), 750(s), 702(s), 662(w), 646(w).
* Corresponding author. Tel.: +65-68745265; fax: +65-68745266.
E-mail address: cvefyy@nus.edu.sg (Y. Feng).
1387-7003/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S1387-7003(03)00014-5

Y.Feng et al./ Inorganic Chemistry Communications 6 (2003) 466–468
467
UV–Vis [kmax(toluene)/nm (10À3e=dm3 molÀ1 cmÀ1)]:
338(9), 420(28), 437(117), 518(1), 570(4), 611(3). 1H
NMR (toluene-d8, )50 °C) d : 9.08 (s, 8H, pyrrole-H),
8.28 (m, 8H, o-H), 7.83 (m, 12H, m,p-H), )6.47 (s, 1H,
GaH).
Single crystals of 1 suitable for X-ray analysis were
obtained by slow evaporation of a solution of the
compound in toluene at )20 °C during a few weeks.
2.2. X-ray structural study of 1
The intensity data of the compound was collected on
Nonius Kappa CCD with Mo-Ka radiation
a
ꢀ
Fig. 1. Electronic absorption spectrum of Ga(TPP)H (solid line) and
Ga(TPP)Cl (dashed line) in toluene.
(k ¼ 0:71073 A) at 293 K. The structure was solved by
direct methods and refined by full-matrix least-squares
based on F 2 using the SHELXL-97 program. All non-
hydrogen atoms were refined anisotropically, while all
hydrogen atoms except M–H were assigned to calcu-
lated positions.
Crystal structure analysis data for 1: [GaC44H28
N4ÞH], Mr ¼ 683:46, tetragonal, I4, a ¼ 13:370ð2Þ, b ¼
ꢀ
ꢀ3
13:370ð2Þ, c ¼ 9:750ð2Þ A, V ¼ 1742:9ð5Þ A , Z ¼ 2,
l ¼ 0:827 mmÀ1, GOF ¼ 1:155, F ð000Þ ¼ 704, R1 ¼
0:0645, wR2 ¼ 0:1731, 118 parameters, 1528 reflections
[I > 2rðIÞ].
3. Results and discussion
The presence of hydride ligand in the compound was
confirmed by the IR spectrum. The Ga–H IR stretch
occurs at 1864 cmÀ1, which locates in the typical region
Fig. 2. ORTEP view of the compound 1 showing the 50% probability
thermal motion ellipsoid. Hydrogen atoms have been omitted for
ꢀ
clarity. Selected bond distances (A): Ga–N 2.035(4), Ga–H 1.48(4),
for other terminal gallium hydrides (ca. 1850–1900 cmÀ1
)
[17,18]. The high-field hydride signal (d: )6.47 ppm) in
the 1H NMR spectrum gives further support for the
existence of hydride. Unlike Ga(TPP)Cl, which shows a
‘‘normal’’ porphyrin electronic spectrum, 1 shows elec-
tronic absorption spectrum belonging to the hyperclass
[19]. The Soret band is split into two bands (labeled band
I and band II), which appear between 338 and 437 nm.
The B(1,0) blue-shifted band is observed at 420 nm, and
the three Q bands are located at 518, 570 and 611 nm.
Band I may be attributed to 4Pz ! egðpꢀÞ transition,
while band II is assigned as a p ! pꢀ electronic transi-
tion. For comparison, the electronic absorption spectra
of [Ga(TPP)Cl] and 1 are shown in Fig. 1.
The molecular structure of 1 is shown in Fig. 2 with
important bond lengths and angles in figure caption. A
crystallographic 4-fold axis passes through Ga and is
perpendicular to the porphyrin plane relating the four
equal parts of the molecule. As observed for Fe(TPP)Cl
[20] and Ga(TPP)Cl [16], the gallium and hydrogen at-
oms are statistically disordered up and down the por-
phyrin macrocyclic plane. The coordination polyhedron
of the metallic atom is a square pyramid and the metal
N–C(1) 1.381(6), N–C(4) 1.378(6), C(1)–C(2) 1.434(7), C(2)–C(3)
1.341(7), C(3)–C(4) 1.446(6), C(4)–C(5) 1.386(7).
ꢀ
little longer than that in Ga(TPP)Cl (0.317(1) A) [16].
ꢀ
The Ga–H distance is 1.48(4) A, which is at the medium
of previously reported terminal Ga–H bonds (ca. 1.4–1.6
ꢀ
A) [21,22]. The bond distances and angles in the por-
phyrinic group are statistically equal to those usually
found.
References
[1] (a) A.J. Downs, Chemistry of Aluminum, Gallium, Indium and
Thallium, Blackie, Glasgow, 1993;
(b) A.J. Downs, C.R. Pulham, Chem. Soc. Rev. (1994) 175, and
references therein.
[2] N.N. Greenwood, A. Storr, M.G.H. Wallbridge, Inorg. Chem. 2
(1963) 1036.
[3] J.L. Atwood, S.G. Bott, F.M. Elms, C. Jones, C.L. Raston, Inorg.
Chem. 30 (1991) 3792.
[4] P.C. Andrews, M.G. Gardiner, C.L. Raston, V.-A. Tolhurst,
Inorg. Chim. Acta 259 (1997) 249.
ꢀ
atom lies 0.46(1) A from the porphyrin plane, which is a

468
Y.Feng et al./ Inorganic Chemistry Communications 6 (2003) 466–468
[5] A. Storr, A.D. Penland, J. Chem. Soc. A (1971) 1237.
[6] (a) A.H. Cowley, F.P. Gabbai, D.A. Atwood, C.J. Carrano, L.M.
[13] J. Setsune, Z. Yoshida, H. Ogoshi, J. Am. Chem. Soc. 99 (1977)
3869.
Mokry, M.R. Bond, J. Am. Chem. Soc. 116 (1994) 1559;
(b) A.H. Cowley, F.P. Gabbai, H.S. Isom, C.J. Carrano, M.R.
Bond, Angew. Chem. Int. Ed. Engl. 33 (1994) 1253;
(c) H.S. Isom, A.H. Cowley, A. Decken, F. Sissingh, S. Corbelin,
R.J. Lagow, Organometallics 14 (1995) 2400.
[14] B.B. Wayland, B.A. Woods, V.M. Minda, J. Chem. Soc. Chem.
Commun. (1982) 634.
[15] V. Grass, D. Lexa, J.-M. Saveant, J. Am. Chem. Soc. 119 (1997)
7526.
[16] A. Coutsolelos, R. Guilard, Polyhedron 5 (1986) 1157.
[17] A.H. Cowley, F.P. Gabbai, D.A. Atwood, C.J. Carrano, L.M.
Mokry, M.R. Bond, J. Am. Chem. Soc. 116 (1994) 1559.
[18] A. Storr, A.D. Penland, J. Chem. Soc. A (1971) 1237.
[19] M. Gouterman, in: D. Dolphin (Ed.), The Porphyrins, vol. III,
Academic Press, New York, 1978 (Chapter 1) and references
therein.
[7] (a) B. Luo, W.L. Gladfelter, Chem. Commun. (2000) 825;
(b) B. Luo, M. Pink, W.L. Gladfelter, Inorg. Chem. 40 (2001)
307.
[8] L. Miinea, D.M. Hoffman, Polyhedron 20 (2001) 2425.
[9] W. Uhl, L. Cuypers, R. Graupner, J. Molter, A. Vester, B.
Neumuller, Z. Anorg. Allg. Chem. 627 (2001) 607.
[10] A.H. Cowley, H.S. Isom, A. Decken, Organometallics 14 (1995)
2589.
[20] J.L. Hoard, G.H. Cohen, M.D. Glick, J. Am. Chem. Soc. 89
(1967) 1992.
[11] A.H. Cowley, F.P. Gabbai, H.S. Isom, A. Decken, J. Organomet.
Chem. 500 (1995) 81.
[21] J.P. Campbell, J.-W. Hwang, V.G. Young Jr., R.B. Von Dreele,
C.J. Cramer, W.L. Gladfelter, J. Am. Chem. Soc. 120 (1998) 521.
[22] R.J. Wehmschulte, J.J. Ellison, K. Ruhlandt-Senge, P.P. Power,
Inorg. Chem. 33 (1994) 6300.
[12] H.S. Isom, A.H. Cowley, A. Decken, F. Sissingh, S. Corbelin, R.J.
Lagow, Organometallics 14 (1995) 2400.