That is a nice question

Use a clean formaldehyde, it should be better

have a nice week end

CD

Try using paraformaldehyde instead and then add the requisite water.

Sometime the precursor RuCl3 is the problem. Look into the water content. From my experience RuCl3-2.5H2O was more reactive than the regular dehydrated RuCl3 wich was unreactive.

The most reliable synthesis doesn't use formaldehyde. Combine 23 g PPh3 and 3g RuCl3xH2O in 350 mL of 2-methoxyethanol and reflux overnight. Allow to cool for an hour or so with stirring then filter under air on a sintered funnel. Wash well with ethanol and then petrol and air dry. The product should be about 9 g and may be pale pink or yellow - either is fine. They are different crystal forms of the same complex and so depending on the relative amounts you may get different proportions of the CO band in the solid state IR - not an issue so far as subsequent reactivity. 

The most likely culprits in the formaldehyde approach are either Ru(CO)3(PPh3)2 (substitution inert) or RuH2(CO)(PPh3)3 which also doesn't have particularly labile phosphines. Sadly, all have IR bands in more or less the same region (ca 1910) so you would need 31P NMR to actually check what you have.

Thanks to everyone for your quick and kind answers. I will try Prof. Hill's method today which seems really suitable. I better understand why it doesn't react anymore if it is indeed composed of Ru(CO)3(PPh3)2 or RuH2(CO)(PPh3)3... Thanks a lot Prof. Hill for your advices ! 

For the moment, I could not find any 31P NMR characterizations in the literature for all the mentionned complexes, would someone of you have any reference mentionning them ? 

Best regards

[RuH2(CO)(PPh)3] appears in the 31P{1H} NMR spectrum as an AX system at 48.6 and 60.7 (2JP,P' = 17 Hz; see also Organometallics 2013, 32, 4440). I do not think that you'll be able to detect the Ru(0) complex by NMR, though...

I am trying to synthesise cis-RuCl2(Me2dcbpy)2 using the method below but I am not forming the product. Can anyone think of what the problem might be? 

A solution of Me2dcbpy (0.492 g, 1.64 mmol) and RuCl3.H2O (0.220 g, 0.841 mmol) in DMF (35 mL) was purged with nitrogen for 15 min. The mixture was heated to 125 oC whilst being vigorously stirred in an oil bath (in darkness). After 2.5 h, the reaction was allowed to cool to room temperature and the DMF was removed on a rotary evaporator to leave a black solid. This solid was stirred in methanol (100 mL) overnight under nitrogen at room temperature. A brown precipitate was collected by filtration