I must admit I only send flat gold, and the leaderboard only refresh the next turn. I guess for gold per turn, you start to send gold the next turn but the leaderboard only refresh the following next turn. Did you wait 2 turns to see?
Side note: Sometimes, when I am the only one competiting, I feel generous and give 1 Gold, securing the victory. Such diplomatic move! But when I have a competitor, I have the choice between: being more generous or... you know: annihilate the competing civilization and be the sole contender. This victory is all about diplomacy.
Too bad there is no such thing as "Soft Power" mechanic in this game yet.