King Frederick William II, who recognized his gifts for diplomacy, sent him in 1787 to Rome to obtain the papal sanction for the appointment of a coadjutor to the bishop of Mainz, with a view to strengthening the German Fürstenbund.

All his power of intrigue was needed in the conduct of these hazardous negotiations, rendered more difficult by the fact that Prussian policy excluded the existence of a strong Polish government.

Despatches in which he expressed his distrust of Bonapartes peaceful professions and his conviction of the danger of the continuance of a neutral policy were intercepted by the first consul, who sought his recall, but eventually accepted him as regular ambassador (1802).

He consistently sought friendly relations between France and Prussia, but he warned his government in 1806 of Napoleon's intention of restoring Hanover to George III and of Joachim Murat's aggressions in Westphalia.

After two unsuccessful attempts at negotiation, the first draft being refused by Napoleon, the second by Frederick William, he joined the Prussian court at Königsberg only to learn that his services were no longer required.

His despatches are edited by Bailleu in Preussen und Frankreicli (Leipzig, 1887, Publikationen aus den preussischen Staatsarchiven).