Polyhedron Vol. 9, No. Z/3, pp. 329-333, 1990

Printed in Great Britain

0277-5387/B $3.00+.00 0 1990 Pergamon Press plc

A PHOSPHOLYL COMPLEX OF INDIUM

TREVOR DOUGLAS and KLAUS H. THEOPOLD*

Department of Chemistry, Baker Laboratory, Cornell University, Ithaca, NY 14853, U.S.A.

and

BRIAN S. HAGGERTY and ARNOLD L. RHEINGOLD*

Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, U.S.A.

Abstract-Reaction of InCl with the phospholyl anion, K( 1%crown-6)+[PC,Me4]-, yielded the indium(II1) ate complex K(18-crown-6)+[(Me4C4P)21nC12]d. Its structure was deter- mined by X-ray diffraction.

Recent interest in the organometallic chemistry of the group 13 elements aluminium, gallium and indium has been fuelled in part by the use of simple alkyls of these elements in the chemical vapour deposition (CVD) of III-V semiconductors (e.g. gallium arsenide, indium phosphide, etc.). ’ Thin films of indium phosphide, for example, are cur- rently grown epitaxially by the high-temperature reaction of InMe, with PHj.2 We are exploring the potential of precursors which contain both of the elements of the desired semiconductor in the same molecule. 3 Herein we report the synthesis and char- acterization of an indium compound containing phosphorus ligands.

The CVD process requires volatile compounds. In designing synthetic targets we were thus attracted to cyclopentadienyl derivatives of indium(I), which have appreciable vapour pressures.4 We reasoned, that substitution of a phosphorus atom for a carbon of the cyclopentadienyl ring (see Scheme 1) might yield a volatile molecule containing both indium and phosphorus which might also feature a frag- mentation pathway with a low activation barrier and relatively unreactive products. The latter would seem to provide a solution to the persistent problem of carbon incorporation into the growing semicon- ductor film.’

* Authors to whom correspondence should be addressed. t Supplementary material available : Atomic coor-

dinates have been deposited with the Director, Cam- bridge Crystallographic Centre.

RESULTS AND DISCUSSION

We have recently described convenient syntheses of the phospholyl anion salts M+[PC4Me4]-.6 Addition of 1.0 equivalent of InCl to a toluene solution of the potassium salt, K(l%crown- 6)+[PC,Me,]-, yielded a dark precipitate and a colourless solution. Filtration, evaporation of sol- vent and recrystallization from THF gave colour- less crystals of a new material. Based on the spec- troscopic and analytical data it was assigned the formula K(18-crown-6)+[(Me,C,P),InCI,I- (l), an ate complex of indium(II1). Complex 1 was isolated in 24% yield based on InCl.

The crystal structure of 1 has been determined by X-ray diffraction and the result is shown in Fig. 1.7 Interatomic distances and angles are listed in Tables 1 and 2, respectively. The coordination environ- ment of indium in the complex anion is a distorted tetrahedron consisting of the two phosphorus atoms of u’-phospholyl ligands and two chlorides. The angles about indium range between 98.7( 1)” (be- tween the chloride ligands) to 13 1.2( 1)” (between the bulky phospholyl groups). The indium-phosphorus bond distances of 2.481(3) and 2.491(3) A closely approximate the sum of the covalent radii of the two elements (In, 1.44 A ; P, 1.06 A). However, they are significantly shorter than the corresponding dis- tances in comparable molecules. Phosphido- bridged dimers of the type [R,In@,-PR;)], feature In-P distances in the range 2.59-2.66 &7 while monomeric molecules exhibit slightly shorter bonds, i.e. 2.588(14), 2.574(11) and 2.613(12) A in the neutral In(PtBu2)37b and 2.585(2), 2.576(2),

329

330 T., DOUGLAS et al.

R

In

..,IR ____)

R-+

\ R a_

R InP +

In ? R

(R = Me, H)

Scheme 1. R

/

Fig. 1. The molecular structure of K(18-crown-6)+[(Me,C,P),InClJ (1) in the crystal.

Table 1. Bond lengths (A)

In-Cl( 1) In-P( 1) In-K C1(2)-K

K--o(2) K--o(4) K-O(6)

P(l)--c(9) P(2)-C(l) C(lvJ2) C(2)-C(3) C(3)-C(4) C(4)-C(8) C(9WAl3) C(lO)--c(l4) c(ll)---c(15)

2.427(4) 2.491(3) 4.258(2) 3.243(4) 2.874(8) 2.821(8) 2.907(7) 1.793(11) 1.772(12) 1.359(16) 1.426(19) 1.318(16) lSll(15) 1.495(15) 1.508(16) 1.515(16)

in-Cl(2) In-P(2) Cl(l)-K

K--o(l) K--o(3) K--o(5) W)_C(l2) P(2)--c(4) C(lk--C(5) C(2)--C(6) C(3)-C(7) C(9)-C(l0) C(lO)--c(ll) C(1 l>-c(l2) C(12)-C(16)

2.441(3) 2.481(3) 3.817(4) 2.800(8) 2.877(6) 2.789(8) 1.761(10) 1.776(11) 1.466(17) 1.523(18) 1.533(20) 1.322(15) 1.430( 15) 1.358(14) 1.513(15)

Cl61

A phospholyl complex of indium

Table 2. Bond angles (“)

331

Cl( l)--In-Cl(Z) C1(2)--In-P( 1) C1(2)--In-P(2) Cl(l)--In-K P( l)-In-K In-Cl( 1)--K In-K-Cl(2) In-P( 1)-C(9)

C(9)-P(l)--c(l2) In-P(2)-C(4)

P(2k--wk-C(2) C(2)-C(l)-w C(l)-C(2)-C(6) C(2)-C(3HX4) C(4)---C(3)--C(7) P(2)_C(4)-C(8) P(l)_C(9)_C(l0) C(lO)--c(9F--C(l3) C(9)--c(lO)--c(l4) c(1o)-c(11)-C(12)

C(l2)--c(ll)--c(l5) P(l)--c(l2)--c(l6)

98.7( 1) 104.6( 1) 103.9(l) 62.8( 1) 81.6(l) 82.8( 1) 34.7( 1) 98.8(3) 90.9(S) 98.8(4)

108.9(9) 127.0( 11) 123.7(12) 113.0(11) 124.0(12) 121.7(9) 109.3(8) 126.O(,lO) 124.3(10) 112.7(9) 123.8(10) 123.5(8)

Cl(l)-In-P(l) Cl( l)-In-P(2) P( I)--In-P(2) C1(2)--In-K P(2)---In-K In-C1(2)---K Cl( l)-K-Cl(2) In-P(l)---C(12) In-P(2)-C( 1)

C( 1 tP(2>--c(4) P(2)--c(lFC(5) C(lw(2>--c(3) C(3)--c(2k-C(6) C(2)-C(3)--c(7) P(2)--c(4>--c(3) C(3)-C(4W(8) P(l)--c(9)--c(l3) C(9)-C(lO)--c(ll) C(1 l)--c(lO)--C(l4) C(lO)-C(llW(l5) P(ltc(l2>-c(ll) C(1 l>--c(l2)-C(l6)

103.8(l) 109.9( 1) 131.2(l) 49.2( 1)

145.5(l) 96.0( 1) 62.5( 1)

101.7(3) 99.9(4) 90.6(5)

123.9(9) 115.2(11) 121.0(11) 122.9( 11) 111.6(9) 126.2(11) 124.4(8) 115.9(10) 119.8(10) 123.4(10) 110.6(8) 125.9(9)

2.586(2) and 2.556(2) A in the ate complex

Li(THF)4[In(PPh2)4].8 The latter values probably reflect the steric bulk of the respective phosphide ligands.

q’-Coordination of the phospholyl moiety to metals is rare.’ However, in this case it parallels the bonding of the all carbon analogue ; i.e. the pentamethylcyclopentadienyl ligand binds to indi- um(II1) in a q’-fashion also.” The bond distances within the heterocycles are very similar to the ones found in the structurally characterized benzyl- phosphole’ ’ and unlike those of the delocalized phospholyl anion found in Li(TMEDA)+pC4 Me4]-.6 The small difference in electronegativity between indium and phosphorus (In, 1.7 ; P, 2.1) also points to the covalent nature of the In-P bonds in 1. The phosphorus atoms assume trigonal pyra- midal configurations, the sum of the bond angles about them being 291.4” for P(1) and 289.3” for P(2). Their lone pairs are apparently not interacting with the indium, making the phospholyl groups formally one-electron donors.

The In-Cl bond length [In-Cl(l), 2.427(4) A ; In-C1(2), 2.441(3) A] are typical for this element combination (sum of covalent radii = 2.43 A) and similar to the distances reported for the [MeInClJ ion (In-Cl,,, 2.40 A).‘* One of the chloride ligands [C1(2)] is interacting weakly with the potassium cation, the distance of 3.244(4) A being only slightly longer than the sum of the ionic radii (K+, 1.33 A ; 1.81 A). The coordination sphere of the potassium

is completed by the six oxygen atoms of the crown ether. The bond distances and angles found for this part of the molecule are normal [see for example the structure of K(18-crown-6)+SCN-].‘3

Complex 1 is obviously the result of a dis- proportionation reaction (see Scheme 2). The desired indium(1) derivative (Me&P)In, while probably formed initially, may be unstable under the reaction conditions. Beachley et al. have found that (q5-&Me,)In decomposes in donor solvents (THF, pyridine), yielding products consistent with a ligand induced disproportionation. I4 It is possible that free crown ether has a similar effect upon (Me,C,P)In. In an attempt to eliminate any donor molecules, we have combined InCl with [LiPC4 MeJ, in toluene. This reaction yielded an off-white precipitate and a yellow solution, from which a yellow powder precipitated upon standing. This material did not contain chloride and the IR spec- trum of the solid as a KBr pellet exhibited bands characteristic of the phospholyl group. The yellow powder was almost completely insoluble in non- polar organic solvents ; however, a very dilute solu- tion in C6D6 exhibited resonances consistent with a coordinated phospholyl moiety [1.84 (s), 2.40, (d, JpH = 11 Hz)]. Addition of THF to the yellow solid initially gave a yellow solution, followed by the formation of a black precipitate (indium metal?) and l,l’-biphospholyl(2). 6 Similarly, an attempted sublimation yielded a grey residue and a white sub- limate of l,l’-biphospholyl. Based on these obser-

332 T. DOUGLAS et al.

ILipc4Me,l, InCl F

2

Scheme 2.

vations, we believe that (Me,C,P)In is indeed formed. However, in non-polar solvents it appar- ently polymerizes, while donor solvents or heating lead to its decomposition.

EXPERIMENTAL

All manipulations involving air-sensitive organo- metallic compounds were carried out in a Vacuum Atmospheres inert-atmosphere box under N2 or on a Schlenk line using Ar or NZ. Solvents were dis- tilled under Nz from purple benzophenone ketyl. NMR: Bruker WM 300 spectrometer (300 MHz for ‘H, 75.47 MHz for 13C and 121.49 MHz for 3 ‘P). Shifts are reported in ppm downfield of TMS (for ‘H and 13C) using the solvent resonances as reference and relative to an external PC13 reference at 219 ppm for 31P IR: Mattson Alpha Centauri . FT-IR. InCl and 18-crown-6 (Aldrich) were used as received.

Potassium(l8 .- crown - 6)bis(chZoro)bis(q’ - 2,3,4,5 - tetramethylphospholyI)indate(I) (1)

To a toluene solution of K( 18-crown-6)PC4Me4 (451 mg, 1.0 mmol) was added InCl (150 mg, 1.0 mmol) and the reaction mixture was stirred at ambi- ent temperature for 1 h. The dark precipitate was filtered off, the solvent evaporated under vacuum, and the residue recrystallized from THF at - 30°C (185 mg, 24% yield). ‘H NMR (CD,CI,) : 3.65 (s, 24 H), 2.07 (d, 12 H, JpH = 10.4 Hz), 1.91 (s, 12 H); “P NMR (CD&l,): -19.16 (s); 13C NMR (CD$l,): 140.61 (s), 133.09 (d, JpC = 15.1 Hz), 70.75 (s), 14.38 (d, JpC = 31 Hz), 14.18 (s). IR (KBr) : 2897 (vs), 2788 (m), 1974 (m), 1471 (s), 1453 (s), 1351 (vs), 1284 (s), 1120 (vs), 962 (vs), 837 (s), 804 (w), 553 (w), 530 (m), 513 (m) cm- ‘. Found : C, 43.91 ; H, 5.72. Calc. for C28H48C121nK06P2 : C, 43.82; H, 6.26%.

Diffractometer Monochromator Scan technique Radiation 20 scan range (“) Data collected Scan speed (” min- ‘) Reflections collected Independent reflections R(merg) (%) Independent reflections

observed Standard reflections Variation in standards

Refinement

RQ 0.0504

R(wfl 0.0574 A/a (max) 0.09 A(P) (e/A- ‘) 0.82 GOF 1.107

NoIN, 9.23

‘Unit cell parameters from the least-squares best fit of the angular settings of 25 reflections (21” < 28 < 26”).

Table 3. Crystallographic data for 1

Crystal parameters

Formula C2,H,,Cl,InKOsP, Space group P2,2,2, Crystal system Orthorhombic

a (A) 10.467(2)

b (A) 13.773(3) c (A) 25.840(6)

V(A’) 3725.4(25) Z 4 Crystal dimensions (mm) 0.10 x 0.28 x 0.48 Crystal colour Colourless D(calc) (g cm- ‘) 1.197 ~(Mo-KoI) (cm- ‘) 10.0 Temperature (“C) 23 T(max)/T(min) 1.13

Data collection

Nicolet R3m Graphite Wyckoff MO-K, 4 < 20 < 45 +h, +k, +I var., 620 5184 4819 4.1

3390 3 std/197 reflns < 2%

A phospholyl complex of indium 333

X-ray structure determination of 1

Crystallographic data are summarized in Table

3. A colourless specimen mounted in a glass capil-

lary was found to belong to the orthorhombic crys- tal system. Systematic absences in the reflection data uniquely determined the space group as P2]2,2,. No correction for absorption was required. The structure was solved by direct methods and refined with anisotropic thermal parameters for all non-hydrogen atoms. Hydro- gen atoms were treated as idealized contributions (dcu = 0.96 A). All software is contained in the SHELXTL library, version 5.1 (G. Sheldrick, Nicolet XRD, Madison, WI).

Acknowledgements-This research was supported by grants from AKZO Corporate Research America Inc. and the New York State Science and Technology Foundation.

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