A novel octa-substituted iridium carbonyl derivative containing the dehydrogenated dppf ligand (dppf=Fe(C5H4PPh2)2): Synthesis and crystal structure of [H4Ir4(CO)4{Fe(C5H 3PPh2)(C5H4P(Ph)C6H 4)}2]

Article abstract of DOI:10.1016/S0020-1693(97)05694-6

The octa-substituted iridium carbonyl derivative [H₄Ir₄(CO)₄{Fe(C₅H ₃PPh₂)(C₅H₄P(Ph)C₆H ₄)}₂] prepared from [Ir₄(CO)₁₂] and dppf consists of a tetrahedral Ir₄ unit and two tetradentate dehydrogenated dppf ligands formed upon ortho-metallation of a cyclopentadienyl and a phenyl ring with each iridium atom coordinated by a carbonyl group, a phosphorus and an ortho-carbon of the dehydrogenated cyclopentadienyl or phenyl group.

Full text of DOI:10.1016/S0020-1693(97)05694-6

Inorganica Chimica Acta 262 (1997) 113–115
Preliminary Communication
A novel octa-substituted iridium carbonyl derivative containing the
dehydrogenated dppf ligand (dppfsFe(C5H4PPh2)2): synthesis and
crystal structure of [H4Ir4(CO)4{Fe(C5H3PPh2)(C5H4P(Ph)C6H4)}2]
Chuen-Her Ueng U, Shu-Mei Lu
Department of Chemistry, National Taiwan Normal University, 88, Sec. 4, Ting-Chow Road, Taipei 117, Taiwan, ROC
Received 23 January 1997; revised 21 February 1997; accepted 1 April 1997
Abstract
The octa-substituted iridium carbonyl derivative [H4Ir4(CO)4{Fe(C5H3PPh2)(C5H4P(Ph)C6H4)}2] prepared from [Ir4(CO)12] and dppf
consists of a tetrahedral Ir4 unit and two tetradentate dehydrogenated dppf ligands formed upon ortho-metallation of a cyclopentadienyl and
a phenyl ring with each iridium atom coordinated by a carbonyl group, a phosphorus and an ortho-carbon of the dehydrogenated cyclopen-
tadienyl or phenyl group.
Keywords: Crystal structures; Iridium complexes; Carbonyl complexes; Hydride complexes; Diphosphine complexes; Cluster complexes
ized by IR, 31P NMR and X-ray single crystal structure
Mono- to hexa-substituted derivatives for the phosphine
containing iridium carbonyl have been published so far. The
di-substituted to hexa-substituted derivatives containing
monodentate phosphines were prepared from [Ir4(CO)12]
and the corresponding ligands by the thermolytic method or
substitution method with [Me3PhCH2N][HIr4(CO)11] or
[Me3PhCH2N]2[Ir4(CO)10]2 as intermediate [1]. The
mono-, di- and tetra-substituted products with diphosphines
were synthesized from [Ir4(CO)12] or [Ir4(CO)11Br]y and
dppm, dppe, dppp or cis-dppe (Ph2P(CH2)nPPh2: ns1,
dppm; ns2, dppe; ns3, dppp; cis-dppescis-
Ph2PCH_CHPPh2) [2]. The tri-substituted derivatives con-
taining triphosphines, HC(PPh2)3 and CH3Si(PEt2)3, were
prepared by the thermolytic method or chemical oxidation
method with Me3NO as initiator [3]. The reported hepta-
substitution derivative [Ir4(CO)5(C8H12)2(C8H10)], which
has no phosphine ligand, was the major product of the reac-
tion between [Ir4(CO)12] and 1,5-cyclooctadiene; however,
the four metal atoms do not retain the tetrahedral unit and are
described as a butterfly geometry associated with alkyne
adducts of tetrametallic clusters or as a closo-octahedral
arrangement of the M4C2 framework from X-ray crystallo-
graphic analysis [4]. In the present work, the unusual octa-
substituted derivative was isolated from the reaction of
[Ir4(CO)12] and dppf in refluxed toluene and was character-
determination.
The title compound was prepared as follows. A mixture of
[Ir4(CO)12] (0.110 g, 0.10 mmol) and dppf (0.110 g, 0.20
mmol) in toluene (20 cm3) was refluxed under nitrogen
atmosphere over a period of 8 h. After the mixture had been
evaporated to dryness under diminished pressure, the crude
product was recrystallized from CH2Cl2/n-hexane. The title
compound was crystallized and filtered first owing to its low
solubility in CH2Cl2 (0.012 g, 5.5%; nmax 1973s,br cmy1
(CO);dP (CDCl3):y34.0, y42.2ppm). Theotherproducts
were further separated by column chromatography.
The crystal data for the title compound are:
C72H56Ir4Fe2O4P4P2CH2Cl2, Mrs2159.5, light yellowish
orange crystals (0.11=0.13=0.21 mm) preparedfromdich-
loromethane/n-hexane by the evaporation method, mono-
clinic, space group P21/c, as19.153(5), bs10.933(4),
3
˚
˚
cs33.339(4) A, bs93.49(2)8, Vs6968(3) A , Zs4,
Dcs2.059 g cmy3, F(000)s4096, Enraf-Nonius CAD4
diffractometer, graphite-monochromated Mo Ka radiation
(ls0.7107 A), m(Mo Ka)s8.21 mmy1, Ts298 K, unit
˚
cell: 25 reflections, 2u range 23.08–32.228. The v/2u mode
was employed with scan widths0.60q0.35 tanu. Three
standard reflections monitored every 2 h: variation on I was
-3%. Of 12 457 reflections measured (3.0-2u-49.98; h,
k, l: y22 to 22, 0 to 12, 0 to 39, respectively), 12 223 were
unique, giving 7074 observed (I)2.5s(I)). An absorption
U Corresponding author.
0020-1693/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved
PII S0020-1693(97)05694-6

114
C.-H. Ueng, S.-M. Lu / Inorganica Chimica Acta 262 (1997) 113–115
correction was made according to experimental c scans
(maximum, minimum transmission factorss0.999, 0.505).
The structure was solved by direct methods. All isotropic H
atoms were calculated after isotropic refinementandincluded
in the structure factor calculation but not refined. Non-hydro-
gen atoms were refined with anisotropic thermal parameters.
The weighting scheme, ws1/s2(Fo), was employed with
s(Fo) from counting statistics. The last least-squares cycle
was calculated with 152 atoms, 830 parameters and 7074
reflections with maximum shift/e.s.d.s0.003. The quantity
minimized was 8w(KFoyFc)2, final R, Rw and S being
0.040, 0.038, and 1.82. The peaks in the final DF map were
y3
y3
˚
˚
2.500 to y1.900 e A . The peaks greater than 1.00 e A
are near the iridium atoms. Correction for secondary extinc-
tion was made with coefficients0.20(2) (length in mm).
Atomic scattering factors were taken from Ref. [5]. The
computing and graphic program used were the NRCVAX
package [6] and ORTEP [7].
All the published phosphine iridium carbonyl derivatives,
except [Ir4(CO)9(HC(PPh2)3)] [3c], contain bridging car-
bonyl groups identified by the CO stretching absorption in
the range 1700–1860 cmy1, although the starting material
[Ir4(CO)12] has only terminal carbonyls [8]. A structure
having no bridging CO groups for the title compound may
be attributed to the bulk and rigidity of the HC(PPh2)3 and
the dppf ligands and to the formation of the bridged metal
hydrides for the title compounds. According to the IR study
[1c,1d,1f,2a], the increase in the substitutionnumberaccom-
panies the decrease in CO stretchingfrequencyfortheiridium
derivatives containing only phosphorus as coordination
atoms (CO peak with highest frequency: 2062–2072, 2029–
2046, 1981–2008 and 1960 cmy1 for di-, tri-, tetra- and hexa-
substituted derivatives, respectively). The frequency of CO
absorption for the title compound (1973 cmy1), which is
higher than that for the hexa-substituted derivative
[Ir4(CO)6(PPh3)4(m3-PPh)] [1d], may be due to the coor-
dinated ortho-carbon of the cyclopentadienylorphenylgroup
and there are no bridging CO groups in the molecule.
Fig. 1. The molecular structure of the title compound. Selected bond lengths
(A) and angles (8): Ir(1)–Ir(2) 2.7097(9), Ir(1)–Ir(3) 2.8643(9), Ir(1)–
˚
Ir(4) 2.9533(9), Ir(2)–Ir(3) 2.937(1), Ir(2)–Ir(4) 2.889(1), Ir(3)–
Ir(4) 2.708(1), Ir(1)–P(1) 2.308(4), Ir(2)–P(2) 2.286(4), Ir(3)–P(3)
2.295(4), Ir(4)–P(4) 2.284(4), Ir(1)–C(1) 1.86(2), Ir(2)–C(2)
1.87(2), Ir(3)–C(3) 1.90(2), Ir(4)–C(4) 1.90(1), Ir(1)–C(2C)
2.12(1), Ir(2)–C(6) 2.07(1), Ir(3)–C(2G) 2.11(1), Ir(4)–C(16)
2.09(1), Ir(2)–Ir(1)–Ir(3) 63.53(3), Ir(2)–Ir(1)–Ir(4) 61.17(2), Ir(3)–
Ir(1)–Ir(4) 55.46(2), Ir(1)–Ir(2)–Ir(3) 60.80(2), Ir(1)–Ir(2)–Ir(4)
63.58(2), Ir(3)–Ir(2)–Ir(4) 55.38(2), Ir(1)–Ir(3)–Ir(2) 55.67(2),
Ir(1)–Ir(3)–Ir(4) 63.94(2), Ir(2)–Ir(3)–Ir(4) 61.40(3), Ir(1)–Ir(4)–
Ir(2) 55.25(2), Ir(1)–Ir(4)–Ir(3) 60.61(2), Ir(2)–Ir(4)–Ir(3) 63.22(3).
and C(4)–O(4) are at the trans position of the attaching Ir–
Ir bonds with OC–Ir–Ir bond angles of 169.2(5), 173.7(5)
and 170.0(4), 178.4(4)8, respectively. The Ir–CO bond
˚
lengths (1.86(2), 1.87(2), 1.89(2) and 1.90(1) A) are
shorter than the other Ir–C bond lengths (2.12(1), 2.11(1),
˚
2.07(1) and 2.09(1) A), since the carbonyl group is known
to be a better p-acceptor than the others. As a whole, the
molecule is quite symmetrical with the same bonding mode
around Ir(1) and Ir(3) and around Ir(2) and Ir(4) and there
seems be a pseudo two-fold rotationalaxisthroughthemiddle
point of Ir(1)–Ir(3) and of Ir(2)–Ir(4).
The molecule shown in Fig. 1 possesses unusual features
arising from the intramolecular reaction. The dppf ligands
become tetradentate ligands on the tetrahedron base sinceone
ortho-cyclopetadienyl and one ortho-phenyl carbon atom
undergo metallation by insertion of iridium atoms. Conse-
quently two CO ligands are replaced by the newly formed Ir–
C bonds and the H atoms migrate to the cluster surface. The
six Ir–Ir bonds are divided into 3 classes: Ir(1)–Ir(2), Ir(3)–
Acknowledgements
˚
Ir(4) (2.7097(9), 2.708(1) A); Ir(1)–Ir(3), Ir(2)–Ir(4)
The authors thank the National Science Council (NSC 85-
2113-M-003-002) for financial support.
˚
(2.8643(9), 2.889(1) A); Ir(1)–Ir(4), Ir(2)–Ir(3)
˚
(2.9533(9), 2.937(1) A). The four larger bond lengths are
due to the formation of bridged metal hydrides and to the
steric hindrance between the two dppf ligands, especially
between phenyl ring B and H and between rings D and F.
The hydridic nature was assumed from electron counting, a
significant elongation of the four Ir–Ir bonds and the presence
of electron density peaks above the long edges. The carbonyl
group C(1)–O(1) and C(2)–O(2) as well as C(3)–O(3)
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