- Email: [email protected]
Mössbauer studies on ferrocene complexes
Journal of Organometallic Chemistry, 456 (1993) 107-l 11
107
JOM 23585
Mijssbauer studies on ferrocene complexes XVIII *. A comparative study of azaferrocenes and phosphaferrocenes and their derivatives by 57Fe MGssbauer and ‘“C NMR spectroscopy A. Houlton,
R.M.G.
Roberts
and J. Silver
Department of Chemistry and Biological Chemistry, University of Essex, Wicenhoe Park, Colchester CO4 3SQ (UK)
J. Zakrzewski Department of Organic Chemistv, (Received
December
lJniuersi& of Lo’di, Narutowicza 68, PL-90-136 Lbdi (Poland)
21, 1992)
Abstract The 13C NMR chemical shifts (61 for azaferrocenes, phosphaferrocenes and their precursor ligands have been used to determine coordination shifts, AS ( = Bcomplex- sligand) for the complexes. For azaferrocenes, AS values were similar to that of ferrocene, but the phosphaferrocenes showed much larger coordination shifts, These observations are discussed in terms of the difference in bonding in these complexes. The “Fe Mossbauer data are reported for a number of azaferrocene derivatives and compared with those for the phosphaferrocene analogues in terms of orbital contributions to the electric field gradient that governs the quadrupole splitting (QS). An excellent correlation is found between QS and the orbital population parameter (2p, - pi), where pz and pi are electronic populations of the e, and e, iron-based orbitals, respectively. Protonation and quaternisation of azaferrocene causes a lowering of QS, in contrast to the slight increase observed for monophosphaferrocene in CF,CO,H solution. The results confirm that protonation at the N atom takes place for azaferrocene. The W(CO), adduct of azaferrocene shows little change in QS from that for azaferrocene, which is interpreted as evidence for back bonding by the tungsten.
1. Introduction Heterocyclic analogues of ferrocene have become the focus of a great deal of research in recent years largely owing to the pioneering work of Mathey [2] on phosphaferrocenes. Less attention has been paid to the corresponding azaferrocenes, in spite of the fact that (C,H,)(C,H,N)Fe was first prepared [3] well before the phosphaferrocenes. For many years l,l’-diazaferrocene proved elusive. However, examples of these ferrocene analogues have now been synthesised and isolated as their adducts with pyrroles bearing bulky 2 and 5 substituents [4,6]. Over the last twelve years we have been interested in the structure of ferrocenes and related compounds and have carried out extensive Correspondence to: Dr. R.M.G. * For Part XVII see ref. 1.
0022-328X/93/$6.00
Roberts
or Dr. J. Silver.
Mossbauer spectroscopic studies in this area (see ref. 1, and preceding papers in this series). We have recently put forward ideas on the bonding in iron sandwich compounds that have rationalised [Fe(cp),] (cp = cyclopentadienyl) with [(q-areneXT-cp)Fe]+ and [CTcomplexes within the same bonding thearene),Fe12+ ory [7,8]. In ferrocene chemistry we have confirmed that substituents on the cp rings increase the Mossbauer quadrupole splitting if they are electron donors and decrease it if they are electron acceptors. These effects have been interpreted in terms of back bonding of iron-based e2 orbitals with antibonding ligand orbitals. We have also reported the differences between the effect of an exocyclic nitrogen and a phosphorus atom in ferrocenylamines and ferrocenylphosphines [91. We concluded that, in ferrocenyl-phosphine derivatives (which show significantly smaller quadrupole splittings than their amino counterparts), lone pair delocalisation 0 1993 - Elsevier Sequoia S.A. All rights reserved
108
.4. ftoulton el al. /' ( omparatit'e ~'tudy of azaferroccnes and pho.sphaferrocenvs
a r o u n d t h e f e r r o c e n y l g r o u p is m u c h lower. W e t h e r e f o r e t u r n e d o u r a t t e n t i o n to c o m p l e x e s in w h i c h t h e h e t e r o a t o m is p a r t o f t h e c y c l o p e n t a d i c n y l l i g a n d . C o n f l i c t i n g M 6 s s b a u e r d a t a for a z a f e r r o c e n c h a v e app e a r e d in t h e l i t e r a t u r e [10,11], a n d this p r o m p t e d us to r e e x a m i n e t h e s e c o m p l e x c s a n d c o m p a r e o u r find,, ings w i t h t h e d a t a o n p h o s p h a f e r r o c e n e s [12].
c a r b o n in t h e ligand. O n e r e m a r k a b l e f i n d i n g is t h a t =16 is a l m o s t c o n s t a n t o v e r a w i d e r a n g e of c h a r g e type and structure.
x __~j
Fe
[:e
[:e 2
- 34.9ppm
36,7, - 33.4, -34,1 ppm 4(72} ~:C3) (Cp)
2. Results and discussion 2.1. J3C N M R spectroscopy T a b l e 1 lists t h e a v a i l a b l e ~3C d a t a for b o t h c o m p l e x e s a n d ligands. T h e pyrrolyl a n d p h o s p h o l y l a n i o n s b o t h s h o w s i m i l a r n o n - u n i f o r m c h e m i c a l shifts. H o w e v e r , for t h e f o r m e r a d o w n f i e l d shift of 9.4 p p m is f o u n d for C2 r e l a t i v e to p y r r o l e itself. T h i s c a n n o t be e x p l a i n e d in t e r m s of c h a r g e d i s t r i b u t i o n , w h i c h w o u l d l e a d to s u b s t a n t i a l s h i e l d i n g . L i p p m a a [14] has sugg e s t e d t h a t t h e s e p a r a m a g n e t i c shifts a r e d u e to a l o w e r i n g in the a v e r a g e e x c i t a t i o n e n e r g y on g o i n g f r o m p y r r o l e to t h e pyrrolyl a n i o n , T h i s is s u p p o r t e d by t h e a c c o m p a n y i n g l a r g e b a t h o c h r o m i c shift o f t h e U V a b s o r p t i o n m a x i m a for s u c h systems. By c o n t r a s t , b o t h ring c a r b o n s o f t h e p h o s p h o l y l a n i o n a r e s h i e l d e d relative to t h o s e in t h e p a r e n t p h o s p h o l e . T h e b o n d i n g in t h e t w o l i g a n d s is t h e r e f o r e r a t h e r d i f f e r e n t , c e r t a i n l y c o m p a r e d w i t h t h e c y c l o p e n t a d i e n y l a n i o n , w h o s e carb o n r e s o n a n c e s a p p e a r well u p f i e l d f r o m t h e i r N a n d P counterparts. M a r k e d c h a n g e s in shift a r e o b s e r v e d o n g o i n g to t h e i r o n ( I I ) c o m p l e x e s of t h e s e ligands. T h e c o o r d i n a tion shift ( A n ) is d e f i n e d as t h e shift o f a p a r t i c u l a r c a r b o n a t o m in t h e c o m p l e x r e l a t i v e to t h a t o f the s a m e
,3/~
.....33.0ppm
T h i s i m p l i e s similar b o n d i n g in t h e s e c o m p l e x e s , and this c o u l d b e r e g a r d e d as i n v o l v i n g a c h a n g e f r o m sp ~ c h a r a c t e r in the l i g a n d to sp" c h a r a c t e r in the c o m p l e x r e s u l t i n g in the s a b s t a m i a l u p f i e l d shifts o b s e r v e d . T h e p h o s p h a f e r r o c c n e s , hovvcvcr, show e x c e p t i o n a l l y l a r g e v a l u e s of k S for t h e p h o s p h o t y l ligand, w h i c h s u g g e s t s a s t r o n g e r interactior~ of l h e C 4 H 4 P c o m p a r e d with t h a t o f C s H s, w h i c h a p p e a r s n o r m a l . T h e r e is also s o m e e v i d e n c e for r e d i s t r i b u t i o n of c h a r g e b e t w c e n rings m the p h o s p h a f e r r o c c n c s . T h e ~ C shift of the C p l i g a n d a p p e a r s d o w n f i e l d f r o m t h o s e in a z a f e r r o c e n e or f e r r o c c n e itself. T h e e f f e c t is p a r t i c u l a r l y n o t i c e a b l c in the case of t h c n o v e l ( C s M % t(Ps)Fe c o m p l e x [20], S i m i l a r c h a r g e t r a n s f e r is also f o u n d in t h e (,?--arcne)(vl.-Cp)t-:e c o m p l e x e s , a n d has b e e n r a t i o n a l i s e d in t e r m s of b a c k b o n d i n g of the iron to t h e a r c n e t i g a n d [7], S u c h n o n - u n i f o r m i t y of c o o r d i n a t i o n shifts has b e e n o b s e r v e d m (rl-cycloh e x a d i e n y t ) ( r l - C p ) F e . [ t e r c the C I ( C 5 ) and C 2 ( C 4 ) s h o w large J(5 v a l u e s c,f - ...... 50 p p m , w h e r e a s (7;3 has
TABLE 1. 13C NMR shifts ~' tot cyclopentadienyl and heterocyclopentadienyl iron sandwich complexes a*xt their amonic precursors Complex
C2
C3
Cs[ts(C~ tl~,)
Coordination shifts b IA,5) C2
CstfsLi C 4 H 4N ki C4H4PLi [3,4-C 4It 2(Ctt 02 PILi (C5115)2 Fe (C 5H s)(C4 H 4N)Fe (C4H4N)2Fe (C~ H ~)(C4 H 4 P)Fe [3,4-C 4tit 2(Ctt 3)2 P]2 Fe [(Cst|5)(3,4-CaII:(Ctt[3)2P)]Fe [C5(CH 3)5]2 Fe [C5(C! t 3)5](P5)Fe [C6tt ¢,)2Fe][PF~,]2 [(CsIlsXC(~H~,)Fe][PF(,] [(C ~H ~XC~,H v)]Fe
126.7 t29.7 128.7 90.0 89.8 77.2 78.2 82.1 _ d
106.0 1197 127.9 7~~ ~ 72.8 79.8 94.8 97. ~ . -- '~
("3
Rot.
('~t t ~{C~,I t r~)
102.8 67.9 68.7 7{).2 71.| 78.5 90.6 94.9 77.4 {88 8) 72.4
- . V~.7 36.9 5..... - %{.5 46.,6
33.4 33.2 39.9 .... 46.6 ?t 4
34.9 - ?4. l ~2.0 31.4 '
.
. d
.
. ~
.... 33.0 ~...4 ( - 3%7) 3{) 4
13 I ..1 15 15 I .~ i7 ~" IS lq 19 20 2{) 21 This work This v,ork
" in ppm from TMS: h At; = 6 complex -. 6 ligand: ' values for the C4Ctt O.i ion arc not a',ailablc: d values of .36 are as follows: C1. C2. -52.4, ('3, + 1.2 ppm.
54.0:
A. Houlton et al. / Comparative study of azaferrocenes and phosphaferrocenes a v a l u e o f + 1.2 p p m . T h e s e results have b e e n interp r e t e d in t e r m s o f p r e f e r e n t i a l o v e r l a p o f the cycloh e x a d i e n y l ligand 7r 2 o r b i t a l with m e t a l dxz, dy z orbitals [22]. 2.2. 57Fe M6ssbauer spectroscopy T h e q u a d r u p o l e splitting p a r a m e t e r for iron c o m plexes is t h o u g h t to d e p e n d on t h e relative p o p u l a t i o n s of t h e e 2 (dx2 y:, dxy) a n d et (dxz, dy z) orbitals. In all iron s a n d w i c h c o m p l e x e s t h e dz2 o r b i t a l a p p e a r s to be fully o c c u p i e d a n d is t h e r e f o r e usually d i s c o u n t e d w h e n c o m p a r i n g Q S values. T h e e 2 o r b i t a l s c o n t r i b u t e twice as strongly to the e l e c t r i c field g r a d i e n t (efg) as the e 1 orbitals, l e a d i n g to the r e l a t i o n s h i p Q S ot 2p2 - Pl
(1)
w h e r e P2 a n d Pl a r e t h e e l e c t r o n i c p o p u l a t i o n s of e 2 a n d e t M O sets, respectively. This r e l a t i o n s h i p can b e verified f r o m c o m p a r i s o n of e x p e r i m e n t a l values of Q S with v a l u e s of P2 a n d p~ c a l c u l a t e d from I N D O S C F M O m e t h o d o l o g y . T h e s e c a l c u l a t i o n s have b e e n carried o u t by C l a c k a n d W a r r e n [23] for u n c h a r g e d complexes. A s s u m i n g t h a t c h a r g e on t h e c e n t r a l m e t a l a t o m affects P2 a n d Pl equally, values o f p o p u l a t i o n d i s t r i b u t i o n c a n b e o b t a i n e d for (r/-C6H6)(r/C s H s ) F e + and ('r/-C6H6)2Fe 2+. T o g e t h e r with t h e values c a l c u l a t e d for f e r r o c e n e , an e x c e l l e n t c o r r e l a t i o n of Q S with (2p2 - P l ) is found, a l b e i t for only t h r e e p o i n t s (r = 0.999), l e a d i n g to t h e r e l a t i o n s h i p QS = 0.192 (2p2 - P l ) + 1.07
(2)
S i m i l a r M O c a l c u l a t i o n s have b e e n m a d e for m o n o p h o s p h a f e r r o c e n e [24]. S u b s t i t u t i n g t h e s e p o p u l a -
109
tion d i s t r i b u t i o n s in t h e above e q u a t i o n s l e a d s to a Q S o f 2.15 m m s 1. This is close to t h e e x p e r i m e n t a l l y o b s e r v e d value of 2.07 m m s - l , a n d s e e m s to c o n f i r m the g e n e r a l a p p l i c a b i l i t y of eqn. (2). F r o m the M 6 s s b a u e r d a t a listed in T a b l e 2 it is c l e a r that o u r values for a z a f e r r o c e n e at 298 K ( s p e c t r u m 3A) a r e m a r k e d l y d i f f e r e n t from t h o s e r e p o r t e d by t h e e a r l i e s t w o r k e r s [10] ( s p e c t r u m 3B). W e s u s p e c t t h a t this d i s c r e p a n c y is d u e to the k n o w n instability of early M 6 s s b a u e r s p e c t r o m e t e r s . O u r values a r e close to t h o s e r e p o r t e d m o r e r e c e n t l y [11]. T h e value of Q S o f 2.51 m m s - 1 is h i g h e r t h a n that for f e r r o c e n e (2.37 m m s - l ) . T h e high Q S for f e r r o c e n e itself is c o n s i d e r e d to derive f r o m filled a n d largely u n p e r t u r b e d e 2 levels giving a large i m b a l a n c e o f e 2 a n d e 1 p o p u l a t i o n s . This m u s t t h e r e f o r e also b e t r u e for a z a f e r r o c e n e , with little mixing of iron d o r b i t a l s even t h o u g h the s y m m e t r y is r e d u c e d from Dsh to C2h. This is in k e e p i n g with t h e t3C c o o r d i n a t i o n shifts, which a r e very similar to t h o s e of f e r r o c e n e . By contrast, m o n o p h o s p h a f e r r o c e n e has a m u c h lower Q S owing to significant o r b i t a l mixing o f dxz_y2 a n d dz2 [26]. This g r e a t e r i n t e r a c t i o n with t h e ligands is t h e p r o b a b l e r e a s o n for the m u c h l a r g e r c o o r d i n a t i o n shifts o b s e r v e d for m o n o p h o s p h a f e r r o c e n e . T h e s e a r e r e m i n i s c e n t of t h o s e o b s e r v e d for t h e cyclohexadienyl c o m p l e x d e s c r i b e d a b o v e in which t h e C H 2 g r o u p lies well o u t of the l i g a n d p l a n e a n d is essentially n o n - b o n d e d to t h e iron. T h e crystal structure of 3 , 4 - d i m e t h y l p h o s p h a f e r r o c e n e [27] shows the P a t o m to be b e n t o u t o f the l i g a n d p l a n e by 0.041 away f r o m the iron, a n d suggests a r a t h e r similar b o n d i n g scheme.
TABLE 2. 57Fe M6ssbauer spectroscopic parameters a for azaferrocenes and related phosphaferrocenes Spectrum no.
Compound
1 2 3
Ferrocene b Ferrocene/CF3COz H c Azaferrocene
3A 3B 4 5 6 7
Azaferrocene Azaferrocene d Azaferrocene/CF3CO2H N-Methylazaferrocenyliodide 2,5-Dimethylazaferrocene e Azaferrocene-W(CO)5 adduct f'g
8
Monophosphaferrocene h Monophosphaferrocene/CF3SO3 H h 2,3,4,5-Tetraphenylmonophosphaferrocene h 2,3,4,5-Tetraphenylmonophosphaferrocene/CF3SO3 H 2,3,4,5-Tetramethylmonophosphaferrocene
9 10 11 12
T 78 80 78 298 298 78 78 78 78 78 80 78 80 78
IS
QS
F!/2
0.52 0.44(1) 0.54(1) 0.30(1) 0.48(1) 0.57 0.54(1) 0.54(1) 0.55(1) 0.58(1) 0.38(2) 0.5l(1) 0.47(1) 0.51(1) 0.52(2) 0.50(1)
2.37 2.59(2) 2.51(1) 2.46(1) 2.14 2.36(1) 2.36(1) 2.48(1) 2.47(3) 0.34(2) 2.07(1) 2.10(1) 2.07(1) 2.12(3) 2.05(1)
0.18(1) 0.14(1) 0.40(5) 0.11(1) 0.18(1) 0.14(1) 0.13(1) 0.16(2) 0.13(2) 0.19(1) 0.13(1) 0.21(1) 0.18(3) 0.16(1)
IS, isomer shift, QS quadrupole splitting, /'1/2 width at half height all in m m s -1, T, K. All data pertain to this work unless otherwise stated. b Data from Ref. 8; c data from Ref. 29; d data from Ref. 9; ° in frozen CH2CI 2 solution; f 55% (absorption area) of component with higher IS; g this material contains an iron(Ill) impurity; h data from Ref. 24.
110
,4. ttoulton et al. / Cornparatit,e study of azaferrocenes and phospha[errocenes
T h e t e m p e r a t u r e d e p e n d e n c e o f Q S for azaferr o c e n e is o u t s i d e e x p e r i m e n t a l e r r o r a n d m a y be due to a slight c h a n g e in solid state structure. T h e s e c o n d m i n o r signal in the 78 K s p e c t r u m of a z a f e r r o c e n e is d u e to an i r o n ( I I ) i m p u r i t y which is not a p p a r e n t at 298 K. It is n o t e w o r t h y in this context that ~H N M R studies on solid a z a f e r r o c e n e have r e v e a l e d a phase c h a n g e at 281 K [28]. A t 77 K t h e r e is evidence of a d i p o l e - g l a s s - l i k e state c a u s e d by the f r e e z i n g out of ligand ring motions. P r o t o n a t i o n of a z a f e r r o e e n e (spect r u m 4) led to a lowering of QS by 0.10 m m s ~. If p r o t o n a t i o n h a d o c c u r r e d on the iron (as with ferr o c e n e itself) an i n c r e a s e in Q S w o u l d have r e s u l t e d . T h u s p r o t o n a t i o n m u s t o c c u r at the N atom. It is k n o w n that, in c o n t r a s t to the p h o s p h a f e r r o c e n e s , azaf e r r o c e n e displays distinct, t h o u g h weak, basic p r o p e r ties ( p K , 7.5, close to t h a t of quinoline), and is r e a d i l y q u a t e r n i s e d by methyl i o d i d e [29]. This indicates that the lone p a i r level is m u c h h i g h e r in e n e r g y in azaferrocenes than phosphaferrocenes. T h e Q S o f the q u a t e r n i s e d a z a f e r r o c e n e ( s p e c t r u m 5) shows a similar d e c r e a s e . P r o t o n a t i o n r e m o v e s electron d e n s i t y f r o m the f i v e - m e m b e r e d ring, which t h e r e fore r e q u i r e s m o r e b a c k b o n d i n g from t h e e2 iron b a s e d o r b i t a l s thus d e p l e t i n g t h e i r p o p u l a t i o n and r e d u c i n g t h e Q S in a c c o r d a n c e with r e l a t i o n s h i p 1. However, the i s o m e r shift (IS) is h i g h e r than t h a t for f e r r o c e n e , suggesting less shielding o f the nucleus by iron 3d and 4p electrons, which will b e p o l a r i s e d t o w a r d s the positive p o l e on the n i t r o g e n . This s h o u l d cause an overall i n c r e a s e in the r a d i a l d i s t r i b u t i o n s of t h e i r orbitals. T h e r e d u c e d Q S for the q u a t e r n i s e d a z a f e r r o c e n e is e x p l a i n e d in similar terms. 2 , 5 - D i m e t h y l a z a f e r r o c e n e ( s p e c t r u m 6) has a very similar Q S to t h a t of a z a f e r r o c e n e itself. Since the i m b a l a n c e b e t w e e n e2 a n d el p o p u l a t i o n s is almost m a x i m a l for f e r r o e e n e a n d a z a f e r r o c e n e , e l e c t r o n - r e leasing s u b s t i t u e n t s a r e unlikely to have much effect. T h e a z a f e r r o c e n e - W ( C O ) 5 a d d u c t ( s p e c t r u m 7) has a Q S i d e n t i c a l to t h a t of a z a f e r r o c e n e itself. This suggests t h a t the n i t r o g e n d o e s not overall possess a significant positive charge, and this could be the result o f b a c k b o n d i n g from the t u n g s t e n to a n t i b o n d i n g orbitals o f the a z a f e r r o c e n e moiety~
3. Experimental section A z a f e r r o c e n e [31] and 2 , 5 - d i m e t h y l a z a f e r r o c e n e [29] w e r e p r e p a r e d by s t a n d a r d m e t h o d s . T h e f o r m e r was m e t h y l a t e d by use of an excess of methyl i o d i d e [32]. 3.1. P r e p a r a t i o n o f ( r l - C s H s ) ( r l - C s H 4 N "
W(CO).s)Fe
A s o l u t i o n of W ( C O ) 6 (0.352 g, 1.0 m m o l ) in dry T H F (15 ml) was p h o t o l y s e d in a Pyrex vessel for 1.5 h
u n d e r argon at r o o m t e m p e r a t u r e with light from a 600 W m e r c u r y lamp. A z a f e r r o c e n e ((1.187 g, 1 retool) was t h e n a d d e d and the solvent e v a p o r a t e d . T h e residue was c h r o m a t o g r a p h c d on silica with dry b e n z e n e as e l u e n t to aft\)rd the c r u d e c o m p l e x c o n t a m i n a t e d with 10% of u n r c a c t e d W(CO)~,. T h e c o m p l e x was purified by extraction with dry C H C I > e v a p o r a t i o n of the extract, a n d r e p e t i t i o n of the c h r o m a t o g r a p h y . It was finally recrystallised from CH ,C! : - h e p t a n e to give 0.210 g of p u r e p r o d u c t (41 {"}). Analysis: Calc. for C ~ a H o N O f F e W: C. 32.91: H, 1.78; N, 2.74. F o u n d : C, 32,84: H, I.(76; N, 2.71%. I R ( C H C I ) ) : ,,,(CO) 206% 1072, 1925 and 1890 cm t. ~H N M R ( C D C I > ~3 in p p m from TMS); 5.63 s (21-t, a - p y r r o l y l H); 4.70 s (2H, /3-pyrrolyl H); 4.47 s (51-t, Cp); 1~C N M R (CDCI3): 201.71 ( , l ( l s ) W - / ~ C ) 153.5 Hz, C O t r a n s to a z a f e r r o c e n e ) , 198,74 (J(ls~W--13C) 131.2 Hz, C O cis to a z a f e r r o c e n e ) , t~4.33 (c,-pyrrolyl C). 72.43 (/3-pyrrolyl C), 70.98 (Cp). 1R s p e c t r a were r e c o r d e d on a Nicolet F T instrum e n t and ~H, ~ ( ; s p e c t r a on a V a r i a n G e m i n i 200 BB s p e c t r o m e t e r , f r e e M 6 s s b a u e r s p e c t r a were o b t a i n e d from frozen solutions and solids and fitted as previously d e s c r i b e d [33-35].
Acknowledgment O n e of us (J.Z.) t h a n k s the Polish C o m m i t t e e of Scientific R e s e a r c h ( K B N ) for financial s u p p o r t for p a r t of this work ((}rant No. 207908101),
References 1 Part XVII, A. ttoulton, P.T. Bishop, R.M,G. Roberts and J. Silver, Z Organomet. Chem., 364 (1989) 381. 2 For an over~iew see, F. Mathey, J. Fischer and J.tt. Nelson: in Structure and Bonding, Springer-Verlag, Berlin, Heidelberg, 1983. p 154. 3 R.B. King and M.B, Bisnettc, hzorg. Chem., 3, (1964) 769. 4 N. Kuhn, E.-M. tlorn, R. Boese and N. Augart, Angew. (Twin., h~t. Ed. Engl., 27 (1988) 1468. 5 N. Kuhn and E'.-M. Horn, bzorg. Chim. Acla, I70 (199(I) 155. e, N. Kuhn, K Jendral, R. Boese and D. BIf.ser. ('hem, Ber.. 127 (1991) 89. 7 A, Houlton, J.R. Miller, R.M.G. Roberts and .I. Silver, J, Chem. Sot., Dalton Trans., ( | 990) 218 l, 8 A. ttoulton, J.R. Miller, R.M.G. Roberts and J. Silver. J, Chem. Soc,, Dalto~z Trans., (1991)467~ 9 A. Houlton, P,T. Bishop, R.M.G. Roberts, J. Silver and M. Herberhold, ,I. Orjcwzomet. Chem.. 364 (1989) 381. 10 R.B. King, L.M. ['pstein and E.W, Gowling, .L Inorg. Nuc[. Chem., 32 (197(t) 44i. 11 R.D. Ernst. D.R, Wilson and R.H. Herber. ,I. Am. Chem. Sot., 106 (1984) 164(~. 12 13. Lukas, R.M.G. Roberts, J. Silver and A.S. Wells, J. Organornel. Chem. 256 (lt,~83) 103, 13 H.-O. Kalinowski, S. 13erger and S. Braun, (arbon-13 NMR Spectrosceg~y, Wile','. New York. Iqb~4.p. 417.
A. Houlton et al. / Comparative study of azaferrocenes and phosphaferrocenes 14 E. Lippmaa, M. Magi, S.S. Novikov, L.I. Khmelnitski, A.S. Prihadko, O.V. Lebedev and L.V. Epishina, Org. Magn. Res., 4 (1972) 197. 15 C. Charrier and F. Mathey, Tetrahedron Lett., 28 (1987) 5015. 16 A.N. Nesmeyanov, E.I. Fedin, L.A. Federov and P.V. Petrovskii, Z Strukt. Khim., 13 (1972) 964. 17 A. Efraty, N. Jubran and A. Goldman, Inorg. Chem., 21 (1982) 868. 18 F. Mathey, J. Organomet. Chem., 139 (1977) 77. 19 G. de Lauzon, F. Mathey and M. Simalty, J. Organomet. Chem., 156 (1978) C33. 20 O.J. Scherer and T. Briick, Angew. Chem., Int. Ed. Engl., 26 (1987) 59. 21 S. Abdul-Rahman, A. Houlton, R.M.G. Roberts and J. Silver, J. Organomet. Chem., 359 (1989) 331. 22 R.M.G. Roberts, unpublished results. 23 D.W. Clack and K.D. Warren, Inorg. Chim. Acta, 30 (1978) 251. 24 N.M. Kosti6 and R.F. Fenske, Organometallics, 2 (1983) 1008. 25 R.M.G. Roberts, J. Silver and A.S. Wells, Inorg. Chim. Acta, 118 (1986) 135.
111
26 C. Guimon, D. Gonbeau, G. Pfister-Gillonzo, G. de Lauzon and F. Mathey, Chem. Phys. Lett., 104 (1984) 560. 27 F. Mathey, A. Mitschler and R. Weiss, J. Amer. Chem. Soc., 99 (1977) 3537. 28 A. Kubo, R. lkeda and D. Nakamura, J. Chem. Soc., Farad. Trans. 3, 82 (1986) 1543. 29 K.K. Joshi, P.L. Pauson, A.R. Quazi and W.H. Stubbs, J. Organomet. Chem., I (1964) 471. 30 R.M.G. Roberts, J. Silver and R.J. Ranson, J. Organomet. Chem., 219 (1981) 233. 31 J. Zakrzewski and C. Gianotti, J. Organomet. Chem., 388 (1990) 175. 32 J. Zakrzewski, Bull. Soc. Chim. Beige, 99 (1990) 357. 33 G. Neshvad, R.M.G. Roberts and J. Silver, J. Organomet. Chem., 221 (1981) 85. 34 M.Y. Hamed, R.C. Hider and J. Silver, lnorg. Chim. Acta, 66 (1982) 13. 35 J. Peterson, J. Silver, M.T. Wilson and I.E.G. Morrison, J. lnorg. Biochem., 13 (1980) 75.
107
JOM 23585
Mijssbauer studies on ferrocene complexes XVIII *. A comparative study of azaferrocenes and phosphaferrocenes and their derivatives by 57Fe MGssbauer and ‘“C NMR spectroscopy A. Houlton,
R.M.G.
Roberts
and J. Silver
Department of Chemistry and Biological Chemistry, University of Essex, Wicenhoe Park, Colchester CO4 3SQ (UK)
J. Zakrzewski Department of Organic Chemistv, (Received
December
lJniuersi& of Lo’di, Narutowicza 68, PL-90-136 Lbdi (Poland)
21, 1992)
Abstract The 13C NMR chemical shifts (61 for azaferrocenes, phosphaferrocenes and their precursor ligands have been used to determine coordination shifts, AS ( = Bcomplex- sligand) for the complexes. For azaferrocenes, AS values were similar to that of ferrocene, but the phosphaferrocenes showed much larger coordination shifts, These observations are discussed in terms of the difference in bonding in these complexes. The “Fe Mossbauer data are reported for a number of azaferrocene derivatives and compared with those for the phosphaferrocene analogues in terms of orbital contributions to the electric field gradient that governs the quadrupole splitting (QS). An excellent correlation is found between QS and the orbital population parameter (2p, - pi), where pz and pi are electronic populations of the e, and e, iron-based orbitals, respectively. Protonation and quaternisation of azaferrocene causes a lowering of QS, in contrast to the slight increase observed for monophosphaferrocene in CF,CO,H solution. The results confirm that protonation at the N atom takes place for azaferrocene. The W(CO), adduct of azaferrocene shows little change in QS from that for azaferrocene, which is interpreted as evidence for back bonding by the tungsten.
1. Introduction Heterocyclic analogues of ferrocene have become the focus of a great deal of research in recent years largely owing to the pioneering work of Mathey [2] on phosphaferrocenes. Less attention has been paid to the corresponding azaferrocenes, in spite of the fact that (C,H,)(C,H,N)Fe was first prepared [3] well before the phosphaferrocenes. For many years l,l’-diazaferrocene proved elusive. However, examples of these ferrocene analogues have now been synthesised and isolated as their adducts with pyrroles bearing bulky 2 and 5 substituents [4,6]. Over the last twelve years we have been interested in the structure of ferrocenes and related compounds and have carried out extensive Correspondence to: Dr. R.M.G. * For Part XVII see ref. 1.
0022-328X/93/$6.00
Roberts
or Dr. J. Silver.
Mossbauer spectroscopic studies in this area (see ref. 1, and preceding papers in this series). We have recently put forward ideas on the bonding in iron sandwich compounds that have rationalised [Fe(cp),] (cp = cyclopentadienyl) with [(q-areneXT-cp)Fe]+ and [CTcomplexes within the same bonding thearene),Fe12+ ory [7,8]. In ferrocene chemistry we have confirmed that substituents on the cp rings increase the Mossbauer quadrupole splitting if they are electron donors and decrease it if they are electron acceptors. These effects have been interpreted in terms of back bonding of iron-based e2 orbitals with antibonding ligand orbitals. We have also reported the differences between the effect of an exocyclic nitrogen and a phosphorus atom in ferrocenylamines and ferrocenylphosphines [91. We concluded that, in ferrocenyl-phosphine derivatives (which show significantly smaller quadrupole splittings than their amino counterparts), lone pair delocalisation 0 1993 - Elsevier Sequoia S.A. All rights reserved
108
.4. ftoulton el al. /' ( omparatit'e ~'tudy of azaferroccnes and pho.sphaferrocenvs
a r o u n d t h e f e r r o c e n y l g r o u p is m u c h lower. W e t h e r e f o r e t u r n e d o u r a t t e n t i o n to c o m p l e x e s in w h i c h t h e h e t e r o a t o m is p a r t o f t h e c y c l o p e n t a d i c n y l l i g a n d . C o n f l i c t i n g M 6 s s b a u e r d a t a for a z a f e r r o c e n c h a v e app e a r e d in t h e l i t e r a t u r e [10,11], a n d this p r o m p t e d us to r e e x a m i n e t h e s e c o m p l e x c s a n d c o m p a r e o u r find,, ings w i t h t h e d a t a o n p h o s p h a f e r r o c e n e s [12].
c a r b o n in t h e ligand. O n e r e m a r k a b l e f i n d i n g is t h a t =16 is a l m o s t c o n s t a n t o v e r a w i d e r a n g e of c h a r g e type and structure.
x __~j
Fe
[:e
[:e 2
- 34.9ppm
36,7, - 33.4, -34,1 ppm 4(72} ~:C3) (Cp)
2. Results and discussion 2.1. J3C N M R spectroscopy T a b l e 1 lists t h e a v a i l a b l e ~3C d a t a for b o t h c o m p l e x e s a n d ligands. T h e pyrrolyl a n d p h o s p h o l y l a n i o n s b o t h s h o w s i m i l a r n o n - u n i f o r m c h e m i c a l shifts. H o w e v e r , for t h e f o r m e r a d o w n f i e l d shift of 9.4 p p m is f o u n d for C2 r e l a t i v e to p y r r o l e itself. T h i s c a n n o t be e x p l a i n e d in t e r m s of c h a r g e d i s t r i b u t i o n , w h i c h w o u l d l e a d to s u b s t a n t i a l s h i e l d i n g . L i p p m a a [14] has sugg e s t e d t h a t t h e s e p a r a m a g n e t i c shifts a r e d u e to a l o w e r i n g in the a v e r a g e e x c i t a t i o n e n e r g y on g o i n g f r o m p y r r o l e to t h e pyrrolyl a n i o n , T h i s is s u p p o r t e d by t h e a c c o m p a n y i n g l a r g e b a t h o c h r o m i c shift o f t h e U V a b s o r p t i o n m a x i m a for s u c h systems. By c o n t r a s t , b o t h ring c a r b o n s o f t h e p h o s p h o l y l a n i o n a r e s h i e l d e d relative to t h o s e in t h e p a r e n t p h o s p h o l e . T h e b o n d i n g in t h e t w o l i g a n d s is t h e r e f o r e r a t h e r d i f f e r e n t , c e r t a i n l y c o m p a r e d w i t h t h e c y c l o p e n t a d i e n y l a n i o n , w h o s e carb o n r e s o n a n c e s a p p e a r well u p f i e l d f r o m t h e i r N a n d P counterparts. M a r k e d c h a n g e s in shift a r e o b s e r v e d o n g o i n g to t h e i r o n ( I I ) c o m p l e x e s of t h e s e ligands. T h e c o o r d i n a tion shift ( A n ) is d e f i n e d as t h e shift o f a p a r t i c u l a r c a r b o n a t o m in t h e c o m p l e x r e l a t i v e to t h a t o f the s a m e
,3/~
.....33.0ppm
T h i s i m p l i e s similar b o n d i n g in t h e s e c o m p l e x e s , and this c o u l d b e r e g a r d e d as i n v o l v i n g a c h a n g e f r o m sp ~ c h a r a c t e r in the l i g a n d to sp" c h a r a c t e r in the c o m p l e x r e s u l t i n g in the s a b s t a m i a l u p f i e l d shifts o b s e r v e d . T h e p h o s p h a f e r r o c c n e s , hovvcvcr, show e x c e p t i o n a l l y l a r g e v a l u e s of k S for t h e p h o s p h o t y l ligand, w h i c h s u g g e s t s a s t r o n g e r interactior~ of l h e C 4 H 4 P c o m p a r e d with t h a t o f C s H s, w h i c h a p p e a r s n o r m a l . T h e r e is also s o m e e v i d e n c e for r e d i s t r i b u t i o n of c h a r g e b e t w c e n rings m the p h o s p h a f e r r o c c n c s . T h e ~ C shift of the C p l i g a n d a p p e a r s d o w n f i e l d f r o m t h o s e in a z a f e r r o c e n e or f e r r o c c n e itself. T h e e f f e c t is p a r t i c u l a r l y n o t i c e a b l c in the case of t h c n o v e l ( C s M % t(Ps)Fe c o m p l e x [20], S i m i l a r c h a r g e t r a n s f e r is also f o u n d in t h e (,?--arcne)(vl.-Cp)t-:e c o m p l e x e s , a n d has b e e n r a t i o n a l i s e d in t e r m s of b a c k b o n d i n g of the iron to t h e a r c n e t i g a n d [7], S u c h n o n - u n i f o r m i t y of c o o r d i n a t i o n shifts has b e e n o b s e r v e d m (rl-cycloh e x a d i e n y t ) ( r l - C p ) F e . [ t e r c the C I ( C 5 ) and C 2 ( C 4 ) s h o w large J(5 v a l u e s c,f - ...... 50 p p m , w h e r e a s (7;3 has
TABLE 1. 13C NMR shifts ~' tot cyclopentadienyl and heterocyclopentadienyl iron sandwich complexes a*xt their amonic precursors Complex
C2
C3
Cs[ts(C~ tl~,)
Coordination shifts b IA,5) C2
CstfsLi C 4 H 4N ki C4H4PLi [3,4-C 4It 2(Ctt 02 PILi (C5115)2 Fe (C 5H s)(C4 H 4N)Fe (C4H4N)2Fe (C~ H ~)(C4 H 4 P)Fe [3,4-C 4tit 2(Ctt 3)2 P]2 Fe [(Cst|5)(3,4-CaII:(Ctt[3)2P)]Fe [C5(CH 3)5]2 Fe [C5(C! t 3)5](P5)Fe [C6tt ¢,)2Fe][PF~,]2 [(CsIlsXC(~H~,)Fe][PF(,] [(C ~H ~XC~,H v)]Fe
126.7 t29.7 128.7 90.0 89.8 77.2 78.2 82.1 _ d
106.0 1197 127.9 7~~ ~ 72.8 79.8 94.8 97. ~ . -- '~
("3
Rot.
('~t t ~{C~,I t r~)
102.8 67.9 68.7 7{).2 71.| 78.5 90.6 94.9 77.4 {88 8) 72.4
- . V~.7 36.9 5..... - %{.5 46.,6
33.4 33.2 39.9 .... 46.6 ?t 4
34.9 - ?4. l ~2.0 31.4 '
.
. d
.
. ~
.... 33.0 ~...4 ( - 3%7) 3{) 4
13 I ..1 15 15 I .~ i7 ~" IS lq 19 20 2{) 21 This work This v,ork
" in ppm from TMS: h At; = 6 complex -. 6 ligand: ' values for the C4Ctt O.i ion arc not a',ailablc: d values of .36 are as follows: C1. C2. -52.4, ('3, + 1.2 ppm.
54.0:
A. Houlton et al. / Comparative study of azaferrocenes and phosphaferrocenes a v a l u e o f + 1.2 p p m . T h e s e results have b e e n interp r e t e d in t e r m s o f p r e f e r e n t i a l o v e r l a p o f the cycloh e x a d i e n y l ligand 7r 2 o r b i t a l with m e t a l dxz, dy z orbitals [22]. 2.2. 57Fe M6ssbauer spectroscopy T h e q u a d r u p o l e splitting p a r a m e t e r for iron c o m plexes is t h o u g h t to d e p e n d on t h e relative p o p u l a t i o n s of t h e e 2 (dx2 y:, dxy) a n d et (dxz, dy z) orbitals. In all iron s a n d w i c h c o m p l e x e s t h e dz2 o r b i t a l a p p e a r s to be fully o c c u p i e d a n d is t h e r e f o r e usually d i s c o u n t e d w h e n c o m p a r i n g Q S values. T h e e 2 o r b i t a l s c o n t r i b u t e twice as strongly to the e l e c t r i c field g r a d i e n t (efg) as the e 1 orbitals, l e a d i n g to the r e l a t i o n s h i p Q S ot 2p2 - Pl
(1)
w h e r e P2 a n d Pl a r e t h e e l e c t r o n i c p o p u l a t i o n s of e 2 a n d e t M O sets, respectively. This r e l a t i o n s h i p can b e verified f r o m c o m p a r i s o n of e x p e r i m e n t a l values of Q S with v a l u e s of P2 a n d p~ c a l c u l a t e d from I N D O S C F M O m e t h o d o l o g y . T h e s e c a l c u l a t i o n s have b e e n carried o u t by C l a c k a n d W a r r e n [23] for u n c h a r g e d complexes. A s s u m i n g t h a t c h a r g e on t h e c e n t r a l m e t a l a t o m affects P2 a n d Pl equally, values o f p o p u l a t i o n d i s t r i b u t i o n c a n b e o b t a i n e d for (r/-C6H6)(r/C s H s ) F e + and ('r/-C6H6)2Fe 2+. T o g e t h e r with t h e values c a l c u l a t e d for f e r r o c e n e , an e x c e l l e n t c o r r e l a t i o n of Q S with (2p2 - P l ) is found, a l b e i t for only t h r e e p o i n t s (r = 0.999), l e a d i n g to t h e r e l a t i o n s h i p QS = 0.192 (2p2 - P l ) + 1.07
(2)
S i m i l a r M O c a l c u l a t i o n s have b e e n m a d e for m o n o p h o s p h a f e r r o c e n e [24]. S u b s t i t u t i n g t h e s e p o p u l a -
109
tion d i s t r i b u t i o n s in t h e above e q u a t i o n s l e a d s to a Q S o f 2.15 m m s 1. This is close to t h e e x p e r i m e n t a l l y o b s e r v e d value of 2.07 m m s - l , a n d s e e m s to c o n f i r m the g e n e r a l a p p l i c a b i l i t y of eqn. (2). F r o m the M 6 s s b a u e r d a t a listed in T a b l e 2 it is c l e a r that o u r values for a z a f e r r o c e n e at 298 K ( s p e c t r u m 3A) a r e m a r k e d l y d i f f e r e n t from t h o s e r e p o r t e d by t h e e a r l i e s t w o r k e r s [10] ( s p e c t r u m 3B). W e s u s p e c t t h a t this d i s c r e p a n c y is d u e to the k n o w n instability of early M 6 s s b a u e r s p e c t r o m e t e r s . O u r values a r e close to t h o s e r e p o r t e d m o r e r e c e n t l y [11]. T h e value of Q S o f 2.51 m m s - 1 is h i g h e r t h a n that for f e r r o c e n e (2.37 m m s - l ) . T h e high Q S for f e r r o c e n e itself is c o n s i d e r e d to derive f r o m filled a n d largely u n p e r t u r b e d e 2 levels giving a large i m b a l a n c e o f e 2 a n d e 1 p o p u l a t i o n s . This m u s t t h e r e f o r e also b e t r u e for a z a f e r r o c e n e , with little mixing of iron d o r b i t a l s even t h o u g h the s y m m e t r y is r e d u c e d from Dsh to C2h. This is in k e e p i n g with t h e t3C c o o r d i n a t i o n shifts, which a r e very similar to t h o s e of f e r r o c e n e . By contrast, m o n o p h o s p h a f e r r o c e n e has a m u c h lower Q S owing to significant o r b i t a l mixing o f dxz_y2 a n d dz2 [26]. This g r e a t e r i n t e r a c t i o n with t h e ligands is t h e p r o b a b l e r e a s o n for the m u c h l a r g e r c o o r d i n a t i o n shifts o b s e r v e d for m o n o p h o s p h a f e r r o c e n e . T h e s e a r e r e m i n i s c e n t of t h o s e o b s e r v e d for t h e cyclohexadienyl c o m p l e x d e s c r i b e d a b o v e in which t h e C H 2 g r o u p lies well o u t of the l i g a n d p l a n e a n d is essentially n o n - b o n d e d to t h e iron. T h e crystal structure of 3 , 4 - d i m e t h y l p h o s p h a f e r r o c e n e [27] shows the P a t o m to be b e n t o u t o f the l i g a n d p l a n e by 0.041 away f r o m the iron, a n d suggests a r a t h e r similar b o n d i n g scheme.
TABLE 2. 57Fe M6ssbauer spectroscopic parameters a for azaferrocenes and related phosphaferrocenes Spectrum no.
Compound
1 2 3
Ferrocene b Ferrocene/CF3COz H c Azaferrocene
3A 3B 4 5 6 7
Azaferrocene Azaferrocene d Azaferrocene/CF3CO2H N-Methylazaferrocenyliodide 2,5-Dimethylazaferrocene e Azaferrocene-W(CO)5 adduct f'g
8
Monophosphaferrocene h Monophosphaferrocene/CF3SO3 H h 2,3,4,5-Tetraphenylmonophosphaferrocene h 2,3,4,5-Tetraphenylmonophosphaferrocene/CF3SO3 H 2,3,4,5-Tetramethylmonophosphaferrocene
9 10 11 12
T 78 80 78 298 298 78 78 78 78 78 80 78 80 78
IS
QS
F!/2
0.52 0.44(1) 0.54(1) 0.30(1) 0.48(1) 0.57 0.54(1) 0.54(1) 0.55(1) 0.58(1) 0.38(2) 0.5l(1) 0.47(1) 0.51(1) 0.52(2) 0.50(1)
2.37 2.59(2) 2.51(1) 2.46(1) 2.14 2.36(1) 2.36(1) 2.48(1) 2.47(3) 0.34(2) 2.07(1) 2.10(1) 2.07(1) 2.12(3) 2.05(1)
0.18(1) 0.14(1) 0.40(5) 0.11(1) 0.18(1) 0.14(1) 0.13(1) 0.16(2) 0.13(2) 0.19(1) 0.13(1) 0.21(1) 0.18(3) 0.16(1)
IS, isomer shift, QS quadrupole splitting, /'1/2 width at half height all in m m s -1, T, K. All data pertain to this work unless otherwise stated. b Data from Ref. 8; c data from Ref. 29; d data from Ref. 9; ° in frozen CH2CI 2 solution; f 55% (absorption area) of component with higher IS; g this material contains an iron(Ill) impurity; h data from Ref. 24.
110
,4. ttoulton et al. / Cornparatit,e study of azaferrocenes and phospha[errocenes
T h e t e m p e r a t u r e d e p e n d e n c e o f Q S for azaferr o c e n e is o u t s i d e e x p e r i m e n t a l e r r o r a n d m a y be due to a slight c h a n g e in solid state structure. T h e s e c o n d m i n o r signal in the 78 K s p e c t r u m of a z a f e r r o c e n e is d u e to an i r o n ( I I ) i m p u r i t y which is not a p p a r e n t at 298 K. It is n o t e w o r t h y in this context that ~H N M R studies on solid a z a f e r r o c e n e have r e v e a l e d a phase c h a n g e at 281 K [28]. A t 77 K t h e r e is evidence of a d i p o l e - g l a s s - l i k e state c a u s e d by the f r e e z i n g out of ligand ring motions. P r o t o n a t i o n of a z a f e r r o e e n e (spect r u m 4) led to a lowering of QS by 0.10 m m s ~. If p r o t o n a t i o n h a d o c c u r r e d on the iron (as with ferr o c e n e itself) an i n c r e a s e in Q S w o u l d have r e s u l t e d . T h u s p r o t o n a t i o n m u s t o c c u r at the N atom. It is k n o w n that, in c o n t r a s t to the p h o s p h a f e r r o c e n e s , azaf e r r o c e n e displays distinct, t h o u g h weak, basic p r o p e r ties ( p K , 7.5, close to t h a t of quinoline), and is r e a d i l y q u a t e r n i s e d by methyl i o d i d e [29]. This indicates that the lone p a i r level is m u c h h i g h e r in e n e r g y in azaferrocenes than phosphaferrocenes. T h e Q S o f the q u a t e r n i s e d a z a f e r r o c e n e ( s p e c t r u m 5) shows a similar d e c r e a s e . P r o t o n a t i o n r e m o v e s electron d e n s i t y f r o m the f i v e - m e m b e r e d ring, which t h e r e fore r e q u i r e s m o r e b a c k b o n d i n g from t h e e2 iron b a s e d o r b i t a l s thus d e p l e t i n g t h e i r p o p u l a t i o n and r e d u c i n g t h e Q S in a c c o r d a n c e with r e l a t i o n s h i p 1. However, the i s o m e r shift (IS) is h i g h e r than t h a t for f e r r o c e n e , suggesting less shielding o f the nucleus by iron 3d and 4p electrons, which will b e p o l a r i s e d t o w a r d s the positive p o l e on the n i t r o g e n . This s h o u l d cause an overall i n c r e a s e in the r a d i a l d i s t r i b u t i o n s of t h e i r orbitals. T h e r e d u c e d Q S for the q u a t e r n i s e d a z a f e r r o c e n e is e x p l a i n e d in similar terms. 2 , 5 - D i m e t h y l a z a f e r r o c e n e ( s p e c t r u m 6) has a very similar Q S to t h a t of a z a f e r r o c e n e itself. Since the i m b a l a n c e b e t w e e n e2 a n d el p o p u l a t i o n s is almost m a x i m a l for f e r r o e e n e a n d a z a f e r r o c e n e , e l e c t r o n - r e leasing s u b s t i t u e n t s a r e unlikely to have much effect. T h e a z a f e r r o c e n e - W ( C O ) 5 a d d u c t ( s p e c t r u m 7) has a Q S i d e n t i c a l to t h a t of a z a f e r r o c e n e itself. This suggests t h a t the n i t r o g e n d o e s not overall possess a significant positive charge, and this could be the result o f b a c k b o n d i n g from the t u n g s t e n to a n t i b o n d i n g orbitals o f the a z a f e r r o c e n e moiety~
3. Experimental section A z a f e r r o c e n e [31] and 2 , 5 - d i m e t h y l a z a f e r r o c e n e [29] w e r e p r e p a r e d by s t a n d a r d m e t h o d s . T h e f o r m e r was m e t h y l a t e d by use of an excess of methyl i o d i d e [32]. 3.1. P r e p a r a t i o n o f ( r l - C s H s ) ( r l - C s H 4 N "
W(CO).s)Fe
A s o l u t i o n of W ( C O ) 6 (0.352 g, 1.0 m m o l ) in dry T H F (15 ml) was p h o t o l y s e d in a Pyrex vessel for 1.5 h
u n d e r argon at r o o m t e m p e r a t u r e with light from a 600 W m e r c u r y lamp. A z a f e r r o c e n e ((1.187 g, 1 retool) was t h e n a d d e d and the solvent e v a p o r a t e d . T h e residue was c h r o m a t o g r a p h c d on silica with dry b e n z e n e as e l u e n t to aft\)rd the c r u d e c o m p l e x c o n t a m i n a t e d with 10% of u n r c a c t e d W(CO)~,. T h e c o m p l e x was purified by extraction with dry C H C I > e v a p o r a t i o n of the extract, a n d r e p e t i t i o n of the c h r o m a t o g r a p h y . It was finally recrystallised from CH ,C! : - h e p t a n e to give 0.210 g of p u r e p r o d u c t (41 {"}). Analysis: Calc. for C ~ a H o N O f F e W: C. 32.91: H, 1.78; N, 2.74. F o u n d : C, 32,84: H, I.(76; N, 2.71%. I R ( C H C I ) ) : ,,,(CO) 206% 1072, 1925 and 1890 cm t. ~H N M R ( C D C I > ~3 in p p m from TMS); 5.63 s (21-t, a - p y r r o l y l H); 4.70 s (2H, /3-pyrrolyl H); 4.47 s (51-t, Cp); 1~C N M R (CDCI3): 201.71 ( , l ( l s ) W - / ~ C ) 153.5 Hz, C O t r a n s to a z a f e r r o c e n e ) , 198,74 (J(ls~W--13C) 131.2 Hz, C O cis to a z a f e r r o c e n e ) , t~4.33 (c,-pyrrolyl C). 72.43 (/3-pyrrolyl C), 70.98 (Cp). 1R s p e c t r a were r e c o r d e d on a Nicolet F T instrum e n t and ~H, ~ ( ; s p e c t r a on a V a r i a n G e m i n i 200 BB s p e c t r o m e t e r , f r e e M 6 s s b a u e r s p e c t r a were o b t a i n e d from frozen solutions and solids and fitted as previously d e s c r i b e d [33-35].
Acknowledgment O n e of us (J.Z.) t h a n k s the Polish C o m m i t t e e of Scientific R e s e a r c h ( K B N ) for financial s u p p o r t for p a r t of this work ((}rant No. 207908101),
References 1 Part XVII, A. ttoulton, P.T. Bishop, R.M,G. Roberts and J. Silver, Z Organomet. Chem., 364 (1989) 381. 2 For an over~iew see, F. Mathey, J. Fischer and J.tt. Nelson: in Structure and Bonding, Springer-Verlag, Berlin, Heidelberg, 1983. p 154. 3 R.B. King and M.B, Bisnettc, hzorg. Chem., 3, (1964) 769. 4 N. Kuhn, E.-M. tlorn, R. Boese and N. Augart, Angew. (Twin., h~t. Ed. Engl., 27 (1988) 1468. 5 N. Kuhn and E'.-M. Horn, bzorg. Chim. Acla, I70 (199(I) 155. e, N. Kuhn, K Jendral, R. Boese and D. BIf.ser. ('hem, Ber.. 127 (1991) 89. 7 A, Houlton, J.R. Miller, R.M.G. Roberts and .I. Silver, J, Chem. Sot., Dalton Trans., ( | 990) 218 l, 8 A. ttoulton, J.R. Miller, R.M.G. Roberts and J. Silver. J, Chem. Soc,, Dalto~z Trans., (1991)467~ 9 A. Houlton, P,T. Bishop, R.M.G. Roberts, J. Silver and M. Herberhold, ,I. Orjcwzomet. Chem.. 364 (1989) 381. 10 R.B. King, L.M. ['pstein and E.W, Gowling, .L Inorg. Nuc[. Chem., 32 (197(t) 44i. 11 R.D. Ernst. D.R, Wilson and R.H. Herber. ,I. Am. Chem. Sot., 106 (1984) 164(~. 12 13. Lukas, R.M.G. Roberts, J. Silver and A.S. Wells, J. Organornel. Chem. 256 (lt,~83) 103, 13 H.-O. Kalinowski, S. 13erger and S. Braun, (arbon-13 NMR Spectrosceg~y, Wile','. New York. Iqb~4.p. 417.
A. Houlton et al. / Comparative study of azaferrocenes and phosphaferrocenes 14 E. Lippmaa, M. Magi, S.S. Novikov, L.I. Khmelnitski, A.S. Prihadko, O.V. Lebedev and L.V. Epishina, Org. Magn. Res., 4 (1972) 197. 15 C. Charrier and F. Mathey, Tetrahedron Lett., 28 (1987) 5015. 16 A.N. Nesmeyanov, E.I. Fedin, L.A. Federov and P.V. Petrovskii, Z Strukt. Khim., 13 (1972) 964. 17 A. Efraty, N. Jubran and A. Goldman, Inorg. Chem., 21 (1982) 868. 18 F. Mathey, J. Organomet. Chem., 139 (1977) 77. 19 G. de Lauzon, F. Mathey and M. Simalty, J. Organomet. Chem., 156 (1978) C33. 20 O.J. Scherer and T. Briick, Angew. Chem., Int. Ed. Engl., 26 (1987) 59. 21 S. Abdul-Rahman, A. Houlton, R.M.G. Roberts and J. Silver, J. Organomet. Chem., 359 (1989) 331. 22 R.M.G. Roberts, unpublished results. 23 D.W. Clack and K.D. Warren, Inorg. Chim. Acta, 30 (1978) 251. 24 N.M. Kosti6 and R.F. Fenske, Organometallics, 2 (1983) 1008. 25 R.M.G. Roberts, J. Silver and A.S. Wells, Inorg. Chim. Acta, 118 (1986) 135.
111
26 C. Guimon, D. Gonbeau, G. Pfister-Gillonzo, G. de Lauzon and F. Mathey, Chem. Phys. Lett., 104 (1984) 560. 27 F. Mathey, A. Mitschler and R. Weiss, J. Amer. Chem. Soc., 99 (1977) 3537. 28 A. Kubo, R. lkeda and D. Nakamura, J. Chem. Soc., Farad. Trans. 3, 82 (1986) 1543. 29 K.K. Joshi, P.L. Pauson, A.R. Quazi and W.H. Stubbs, J. Organomet. Chem., I (1964) 471. 30 R.M.G. Roberts, J. Silver and R.J. Ranson, J. Organomet. Chem., 219 (1981) 233. 31 J. Zakrzewski and C. Gianotti, J. Organomet. Chem., 388 (1990) 175. 32 J. Zakrzewski, Bull. Soc. Chim. Beige, 99 (1990) 357. 33 G. Neshvad, R.M.G. Roberts and J. Silver, J. Organomet. Chem., 221 (1981) 85. 34 M.Y. Hamed, R.C. Hider and J. Silver, lnorg. Chim. Acta, 66 (1982) 13. 35 J. Peterson, J. Silver, M.T. Wilson and I.E.G. Morrison, J. lnorg. Biochem., 13 (1980) 75.